Method and user equipment for receiving downlink signal and method and base station for transmitting downlink signal

ABSTRACT

The present invention provides: a base station for repeatedly transmitting a physical downlink control channel (PDCCH) during a first subframe bundle comprising a plurality of subframes, and transmitting a PDSCH related to the PDCCH; and user equipment for receiving the PDCCH and the PDSCH. The PDSCH can be transmitted to the user equipment starting from subframe n+k, which is the k th  subframe after the last subframe n−1 in the first subframe bundle, wherein k is an integer bigger than 0. The first subframe bundle may begin from a predetermined or fixed position.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0] This application is a continuation of U.S. patent application Ser.No. 14/428,909, filed on Mar. 17, 2015, now U.S. Pat. No. 9,485,763,which is the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2014/000387, filed on Jan. 14, 2014, which claimsthe benefit of U.S. Provisional Application No. 61/752,444, filed onJan. 14, 2013, 61/810,678, filed on Apr. 10, 2013, 61/822,416, filed onMay 12, 2013, 61/862,518, filed on Aug. 6, 2013, 61/883,214, filed onSep. 27, 2013 and 61/886,673, filed Oct. 4, 2013, the contents of whichare all hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting or receiving a signaland an apparatus therefor.

TECHNICAL FIELD

With appearance and spread of machine-to-machine (M2M) communication anda variety of devices such as smartphones and tablet PCs and technologydemanding a large amount of data transmission, data throughput needed ina cellular network has rapidly increased. To satisfy such rapidlyincreasing data throughput, carrier aggregation technology, cognitiveradio technology, etc. for efficiently employing more frequency bandsand multiple input multiple output (MIMO) technology, multi-base station(BS) cooperation technology, etc. for raising data capacity transmittedon limited frequency resources have been developed.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). A base station (BS) and a userequipment (UE) transmit and receive data and/or control informationscheduled on a prescribed time unit basis, e.g. on a subframe basis. Thedata is transmitted and received through a data region configured in aUL/DL subframe and the control information is transmitted and receivedthrough a control region configured in the UL/DL subframe. To this end,various physical channels carrying radio signals are formed in the UL/DLsubframe. In contrast, carrier aggregation technology serves to use awider UL/DL bandwidth by aggregating a plurality of UL/DL frequencyblocks in order to use a broader frequency band so that more signalsrelative to signals when a single carrier is used can be simultaneouslyprocessed.

In addition, a communication environment has evolved into increasingdensity of nodes accessible by a user at the periphery of the nodes. Anode refers to a fixed point capable of transmitting/receiving a radiosignal to/from the UE through one or more antennas. A communicationsystem including high-density nodes may provide a better communicationservice to the UE through cooperation between the nodes.

DETAILED DESCRIPTION OF THE INVENTION Technical Problems

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solutions

In an aspect of the present invention, provided herein is a method forreceiving a downlink signal by a user equipment, including performingrepetitive reception of a physical downlink control channel (PDCCH)during a first subframe bundle including multiple subframes.

In another aspect of the present invention, provided herein is a userequipment for receiving a downlink signal, including a radio frequency(RF) unit and a processor configured to control the RF unit, wherein theprocessor controls the RF unit to perform repetitive reception of aphysical downlink control channel (PDCCH) during a first subframe bundleincluding multiple subframes.

In still another aspect of the present invention, provided herein is amethod for transmitting a downlink signal by a user equipment, includingperforming repetitive transmission of a physical downlink controlchannel (PDCCH) during a first subframe bundle including multiplesubframes.

In a further aspect of the present invention, provided herein is a basestation for transmitting a downlink signal, including a radio frequency(RF) unit and a processor configured to control the RF unit, wherein theprocessor controls the RF unit to perform repetitive transmission of aphysical downlink control channel (PDCCH) during a first subframe bundleincluding multiple subframes.

In each aspect of the present invention, transmission of a physicaldownlink shared channel (PDSCH) associated with the PDCCH may beperformed starting from a subframe n+k corresponding to a k-th subframeafter a last subframe n−1 of the first subframe bundle, wherein k is aninteger greater than 0.

In each aspect of the present invention, a start subframe of the firstsubframe bundle may be started at a preset location or a fixed location.

In each aspect of the present invention, a size of the first subframebundle may be a preset value or a fixed value.

In each aspect of the present invention, repetitive transmission of thePDSCH may be performed during a second subframe bundle starting from thesubframe n+k.

In each aspect of the present invention, information indicating at leastone of a transmission period of the second subframe bundle, an offset inthe transmission period of the second subframe bundle, and a size of thesecond subframe bundle may be transmitted to the user equipment.

In each aspect of the present invention, transmission of a physicalbroadcast channel (PBCH) may be further performed.

In each aspect of the present invention, the user equipment may assumethat the PDSCH is not transmitted in a resource of the PBCH.

In each aspect of the present invention, information about a startlocation of a third subframe bundle for repetitive transmission ofacknowledgement (ACK)/negative acknowledgement (NACK) information forthe PDSCH and a size of the third subframe bundle may be furthertransmitted to the user equipment.

The above technical solutions are merely some parts of the embodimentsof the present invention and various embodiments into which thetechnical features of the present invention are incorporated can bederived and understood by persons skilled in the art from the followingdetailed description of the present invention.

Advantageous Effect

According to the present invention, uplink/downlink signals can beefficiently transmitted/received. Therefore, overall throughput of aradio communication system can be improved.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot ina wireless communication system.

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS).

FIG. 4 illustrates the structure of a DL subframe used in a wirelesscommunication system.

FIG. 5 illustrates configuration of cell specific reference signals(CRSs) and user specific reference signals (UE-RS).

FIG. 6 illustrates the structure of a UL subframe used in a wirelesscommunication system.

FIG. 7 illustrates a physical downlink control channel (PDCCH) or anenhanced PDCCH (EPDCCH), and a data channel scheduled by PDCCH/EPDCCH.

FIG. 8 is a block diagram illustrating elements of a transmitting device10 and a receiving device 20 for implementing the present invention.

FIG. 9 illustrates an overview of physical channel processing.

FIG. 10 illustrates a signal transmission/reception method according toembodiment A of the present invention.

FIG. 11 illustrates another signal transmission/reception methodaccording to embodiment A of the present invention.

FIG. 12 illustrates still another signal transmission/reception methodaccording to embodiment A of the present invention.

FIG. 13 illustrates a signal transmission/reception method according toembodiment B of the present invention.

FIG. 14 illustrates a signal transmission/reception method according toembodiment C of the present invention.

FIGS. 15, 16, and 17 illustrate signal transmission/reception methodsaccording to embodiment D of the present invention.

FIG. 18 illustrates a signal transmission/reception method according toembodiment E of the present invention.

FIG. 19 illustrates a signal transmission/reception method according toembodiment F of the present invention.

FIG. 20 illustrates a signal transmission/reception method according toembodiment G of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port, avirtual antenna, or an antenna group. A node may be referred to as apoint. In the multi-node system, the same cell identity (ID) ordifferent cell IDs may be used to transmit/receive signals to/from aplurality of nodes. If the plural nodes have the same cell ID, each ofthe nodes operates as a partial antenna group of one cell. If the nodeshave different cell IDs in the multi-node system, the multi-node systemmay be regarded as a multi-cell (e.g. a macro-cell/femto-cell/pico-cell)system. If multiple cells formed respectively by multiple nodes areconfigured in an overlaid form according to coverage, a network formedby the multiple cells is referred to as a multi-tier network. A cell IDof an RRH/RRU may be the same as or different from a cell ID of an eNB.When the RRH/RRU and the eNB use different cell IDs, both the RRH/RRUand the eNB operate as independent eNBs.

In the multi-node system, one or more eNBs or eNB controllers connectedto multiple nodes may control the nodes such that signals aresimultaneously transmitted to or received from a UE through some or allnodes. While there is a difference between multi-node systems accordingto the nature of each node and implementation form of each node,multi-node systems are discriminated from single node systems (e.g. acentralized antenna system (CAS), conventional MIMO systems,conventional relay systems, conventional repeater systems, etc.) since aplurality of nodes provides communication services to a UE in apredetermined time-frequency resource. Accordingly, embodiments of thepresent invention with respect to a method of performing coordinateddata transmission using some or all nodes may be applied to varioustypes of multi-node systems. For example, a node refers to an antennagroup spaced apart from another node by a predetermined distance ormore, in general. However, embodiments of the present invention, whichwill be described below, may even be applied to a case in which a noderefers to an arbitrary antenna group irrespective of node interval. Inthe case of an eNB including an X-pole (cross-polarized) antenna, forexample, the embodiments of the preset invention are applicable on theassumption that the eNB controls a node composed of an H-pole antennaand a node composed of a V-pole antenna.

A communication scheme through which signals are transmitted/receivedvia a plurality of transmit (Tx)/receive (Rx) nodes, signals aretransmitted/received via at least one node selected from a plurality ofTx/Rx nodes, or a node transmitting a DL signal is discriminated from anode transmitting a UL signal is called multi-eNB MIMO or coordinatedmulti-point transmission/reception (CoMP). Coordinated transmissionschemes from among CoMP communication schemes may be broadly categorizedinto joint processing (JP) and scheduling coordination. The former maybe divided into joint transmission (JT)/joint reception (JR) and dynamicpoint selection (DPS) and the latter may be divided into coordinatedscheduling (CS) and coordinated beamforming (CB). DPS may be calleddynamic cell selection (DCS). When JP is performed, a wider variety ofcommunication environments can be formed, compared to other CoMPschemes. JT refers to a communication scheme by which a plurality ofnodes transmits the same stream to a UE and JR refers to a communicationscheme by which a plurality of nodes receive the same stream from theUE. The UE/eNB combine signals received from the plurality of nodes torestore the stream. In the case of JT/JR, signal transmissionreliability can be improved according to transmit diversity since thesame stream is transmitted to/from a plurality of nodes. In JP, DPSrefers to a communication scheme by which a signal istransmitted/received through a node selected from a plurality of nodesaccording to a specific rule. In the case of DPS, signal transmissionreliability can be improved because a node having a good channel statebetween the node and the UE is selected as a communication node.

In the present invention, a cell refers to a prescribed geographicalarea to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell. Furthermore, channelstatus/quality of a specific cell refers to channel status/quality of achannel or communication link formed between an eNB or node whichprovides a communication service to the specific cell and a UE. The UEmay measure DL channel state received from a specific node usingcell-specific reference signal(s) (CRS(s)) transmitted on a CRS resourceand/or channel state information reference signal(s) (CSI-RS(s))transmitted on a CSI-RS resource, allocated by antenna port(s) of thespecific node to the specific node. Meanwhile, a 3GPP LTE/LTE-A systemuses the concept of a cell in order to manage radio resources and a cellassociated with the radio resources is distinguished from a cell of ageographic region.

Recently, to use a wider frequency band in recent wireless communicationsystems, introduction of carrier aggregation (or BW aggregation)technology that uses a wider UL/DL BW by aggregating a plurality ofUL/DL frequency blocks has been discussed. A carrier aggregation (CA) isdifferent from an orthogonal frequency division multiplexing (OFDM)system in that DL or UL communication is performed using a plurality ofcarrier frequencies, whereas the OFDM system carries a base frequencyband divided into a plurality of orthogonal subcarriers on a singlecarrier frequency to perform DL or UL communication. Hereinbelow, eachof carriers aggregated by carrier aggregation will be referred to as acomponent carrier (CC). The “cell” associated with the radio resourcesis defined by combination of downlink resources and uplink resources,that is, combination of DL CC and UL CC. The cell may be configured bydownlink resources only, or may be configured by downlink resources anduplink resources. If carrier aggregation is supported, linkage between acarrier frequency of the downlink resources (or DL CC) and a carrierfrequency of the uplink resources (or UL CC) may be indicated by systeminformation. For example, combination of the DL resources and the ULresources may be indicated by linkage of system information block type 2(SIB2). In this case, the carrier frequency means a center frequency ofeach cell or CC. A cell operating on a primary frequency may be referredto as a primary cell (Pcell) or PCC, and a cell operating on a secondaryfrequency may be referred to as a secondary cell (Scell) or SCC. Thecarrier corresponding to the Pcell on downlink will be referred to as adownlink primary CC (DL PCC), and the carrier corresponding to the Pcellon uplink will be referred to as an uplink primary CC (UL PCC). A Scellmeans a cell that may be configured after completion of radio resourcecontrol (RRC) connection establishment and used to provide additionalradio resources. The Scell may form a set of serving cells for the UEtogether with the Pcell in accordance with capabilities of the UE. Thecarrier corresponding to the Scell on the downlink will be referred toas downlink secondary CC (DL SCC), and the carrier corresponding to theScell on the uplink will be referred to as uplink secondary CC (UL SCC).Although the UE is in RRC-CONNECTED state, if it is not configured bycarrier aggregation or does not support carrier aggregation, a singleserving cell configured by the Pcell only exists.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide service using a carrier and a “cell” of a radioresource is associated with bandwidth (BW) which is a frequency rangeconfigured by the carrier. Since DL coverage, which is a range withinwhich the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, the coverage of the node may be associated with coverage of the“cell” of a radio resource used by the node. Accordingly, the term“cell” may be used to indicate service coverage of the node sometimes, aradio resource at other times, or a range that a signal using a radioresource can reach with valid strength at other times.

3GPP LTE/LTE-A standards define DL physical channels corresponding toresource elements carrying information derived from a higher layer andDL physical signals corresponding to resource elements which are used bya physical layer but which do not carry information derived from ahigher layer. For example, a physical downlink shared channel (PDSCH), aphysical broadcast channel (PBCH), a physical multicast channel (PMCH),a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid ARQ indicatorchannel (PHICH) are defined as the DL physical channels, and a referencesignal and a synchronization signal are defined as the DL physicalsignals. A reference signal (RS), also called a pilot, refers to aspecial waveform of a predefined signal known to both a BS and a UE. Forexample, a cell-specific RS (CRS), a UE-specific RS (UE-RS), apositioning RS (PRS), and channel state information RS (CSI-RS) may bedefined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A standards define ULphysical channels corresponding to resource elements carryinginformation derived from a higher layer and UL physical signalscorresponding to resource elements which are used by a physical layerbut which do not carry information derived from a higher layer. Forexample, a physical uplink shared channel (PUSCH), a physical uplinkcontrol channel (PUCCH), and a physical random access channel (PRACH)are defined as the UL physical channels, and a demodulation referencesignal (DM RS) for a UL control/data signal and a sounding referencesignal (SRS) used for UL channel measurement are defined as the ULphysical signals.

In the present invention, a physical downlink control channel (PDCCH), aphysical control format indicator channel (PCFICH), a physical hybridautomatic retransmit request indicator channel (PHICH), and a physicaldownlink shared channel (PDSCH) refer to a set of time-frequencyresources or resource elements (REs) carrying downlink controlinformation (DCI), a set of time-frequency resources or REs carrying acontrol format indicator (CFI), a set of time-frequency resources or REscarrying downlink acknowledgement (ACK)/negative ACK (NACK), and a setof time-frequency resources or REs carrying downlink data, respectively.In addition, a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a physical random access channel(PRACH) refer to a set of time-frequency resources or REs carryinguplink control information (UCI), a set of time-frequency resources orREs carrying uplink data and a set of time-frequency resources or REscarrying random access signals, respectively. In the present invention,in particular, a time-frequency resource or RE that is assigned to orbelongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to asPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,respectively. Therefore, in the present invention, PUCCH/PUSCH/PRACHtransmission of a UE is conceptually identical to UCI/uplink data/randomaccess signal transmission on PUSCH/PUCCH/PRACH, respectively. Inaddition, PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB isconceptually identical to downlink data/DCI transmission onPDCCH/PCFICH/PHICH/PDSCH, respectively.

In addition, in the present invention, a PBCH/(e)PDCCH/PDSCH/PUCCH/PUSCHregion refers to a time-frequency resource region to whichPBCH/(e)PDCCH/PDSCH/PUCCH/PUSCH has been mapped or may be mapped.

Hereinafter, OFDM symbol/subcarrier/RE to or for whichCRS/DMRS/CSI-RS/SRS/UE-RS/TRS is assigned or configured will be referredto as CRS/DMRS/CSI-RS/SRS/UE-RS/TRS symbol/carrier/subcarrier/RE. Forexample, an OFDM symbol to or for which a tracking RS (TRS) is assignedor configured is referred to as a TRS symbol, a subcarrier to or forwhich the TRS is assigned or configured is referred to as a TRSsubcarrier, and an RE to or for which the TRS is assigned or configuredis referred to as a TRS RE. In addition, a subframe configured fortransmission of the TRS is referred to as a TRS subframe. Moreover, asubframe in which a broadcast signal is transmitted is referred to as abroadcast subframe or a PBCH subframe and a subframe in which asynchronization signal (e.g. PSS and/or SSS) is transmitted is referredto a synchronization signal subframe or a PSS/SSS subframe. OFDMsymbol/subcarrier/RE to or for which PSS/SSS is assigned or configuredis referred to as PSS/SSS symbol/subcarrier/RE, respectively.

In the present invention, a CRS port, a UE-RS port, a CSI-RS port, and aTRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna ports configured to transmit CRSs may bedistinguished from each other by the locations of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the locations of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the locationsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a patternof REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a predetermined resourceregion. In the present invention, both a DMRS and a UE-RS refer to RSsfor demodulation and, therefore, the terms DMRS and UE-RS are used torefer to RSs for demodulation.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

Specifically, FIG. 1(a) illustrates an exemplary structure of a radioframe which can be used in frequency division multiplexing (FDD) in 3GPPLTE/LTE-A and FIG. 1(b) illustrates an exemplary structure of a radioframe which can be used in time division multiplexing (TDD) in 3GPPLTE/LTE-A.

Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms(307,200T_(s)) in duration. The radio frame is divided into 10 subframesof equal size. Subframe numbers may be assigned to the 10 subframeswithin one radio frame, respectively. Here, T_(s) denotes sampling timewhere T_(s)=1/(2048*15 kHz). Each subframe is 1 ms long and is furtherdivided into two slots. 20 slots are sequentially numbered from 0 to 19in one radio frame. Duration of each slot is 0.5 ms. A time interval inwhich one subframe is transmitted is defined as a transmission timeinterval (TTI). Time resources may be distinguished by a radio framenumber (or radio frame index), a subframe number (or subframe index), aslot number (or slot index), and the like.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

Table 1 shows an exemplary UL-DL configuration within a radio frame inTDD mode.

TABLE 1 Downlink-to-Uplink Uplink-downlink Switch-point Subframe numberconfiguration periodicity 0 1 2 3 4 5 6 7 8 9 0  5 ms D S U U U D S U UU 1  5 ms D S U U D D S U U D 2  5 ms D S U D D D S U D D 3 10 ms D S UU U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D

In Table 1, D denotes a DL subframe, U denotes a UL subframe, and Sdenotes a special subframe. The special subframe includes three fields,i.e. downlink pilot time slot (DwPTS), guard period (GP), and uplinkpilot time slot (UpPTS). DwPTS is a time slot reserved for DLtransmission and UpPTS is a time slot reserved for UL transmission.Table 2 shows an example of the special subframe configuration.

TABLE 2 Normal Extended cyclic prefix in downlink cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended cyclic cycliccyclic cyclic Special subframe prefix in prefix in prefix in prefix inconfiguration DwPTS uplink uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 2 illustrates the structure of a DL/UL slot structure in a wirelesscommunication system. In particular, FIG. 2 illustrates the structure ofa resource grid of a 3GPP LTE/LTE-A system. One resource grid is definedper antenna port.

Referring to FIG. 2, a slot includes a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. The OFDMsymbol may refer to one symbol duration. Referring to FIG. 2, a signaltransmitted in each slot may be expressed by a resource grid includingN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. N^(DL) _(RB) denotes the number of RBs in a DL slot and N^(UL)_(RB) denotes the number of RBs in a UL slot. N^(DL) _(RB) and N^(UL)_(RB) depend on a DL transmission bandwidth and a UL transmissionbandwidth, respectively. N^(DL) _(symb) denotes the number of OFDMsymbols in a DL slot, N^(UL) _(symb) denotes the number of OFDM symbolsin a UL slot, and N^(RB) _(sc) denotes the number of subcarriersconfiguring one RB.

An OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access schemes. The number of OFDM symbols included in one slotmay be varied according to channel bandwidths and CP lengths. Forexample, in a normal cyclic prefix (CP) case, one slot includes 7 OFDMsymbols. In an extended CP case, one slot includes 6 OFDM symbols.Although one slot of a subframe including 7 OFDM symbols is shown inFIG. 2 for convenience of description, embodiments of the presentinvention are similarly applicable to subframes having a differentnumber of OFDM symbols. Referring to FIG. 2, each OFDM symbol includesN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers in the frequency domain. Thetype of the subcarrier may be divided into a data subcarrier for datatransmission, a reference signal (RS) subcarrier for RS transmission,and a null subcarrier for a guard band and a DC component. The nullsubcarrier for the DC component is unused and is mapped to a carrierfrequency f₀ in a process of generating an OFDM signal or in a frequencyup-conversion process. The carrier frequency is also called a centerfrequency f_(c).

One RB is defined as N^(DL/UL) _(symb) (e.g. 7) consecutive OFDM symbolsin the time domain and as N^(RB) _(sc) (e.g. 12) consecutive subcarriersin the frequency domain. For reference, a resource composed of one OFDMsymbol and one subcarrier is referred to a resource element (RE) ortone. Accordingly, one RB includes N^(DL/UL) _(symb)*N^(RB) _(sc) REs.Each RE within a resource grid may be uniquely defined by an index pair(k, l) within one slot. k is an index ranging from 0 to N^(DL/UL)_(RB)*N^(RB) _(sc)−1 in the frequency domain, and l is an index rangingfrom 0 to N^(DL/UL) _(symb)1−1 in the time domain.

Meanwhile, one RB is mapped to one physical resource block (PRB) and onevirtual resource block (VRB). A PRB is defined as N^(DL) _(symb) (e.g.7) consecutive OFDM or SC-FDM symbols in the time domain and N^(RB)_(sc) (e.g. 12) consecutive subcarriers in the frequency domain.Accordingly, one PRB is configured with N^(DL/UL) _(symb)*N^(RB) _(sc)REs. In one subframe, two RBs each located in two slots of the subframewhile occupying the same N^(RB) _(sc) consecutive subcarriers arereferred to as a physical resource block (PRB) pair. Two RBs configuringa PRB pair have the same PRB number (or the same PRB index).

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS). Specifically, FIG. 3 illustrates a radioframe structure for transmission of an SS and a PBCH in frequencydivision duplex (FDD), wherein FIG. 3(a) illustrates transmissionlocations of an SS and a PBCH in a radio frame configured as a normalcyclic prefix (CP) and FIG. 3(b) illustrates transmission locations ofan SS and a PBCH in a radio frame configured as an extended CP.

If a UE is powered on or newly enters a cell, the UE performs an initialcell search procedure of acquiring time and frequency synchronizationwith the cell and detecting a physical cell identity N^(cell) _(ID) ofthe cell. To this end, the UE may establish synchronization with the eNBby receiving synchronization signals, e.g. a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS), from the eNBand obtain information such as a cell identity (ID).

An SS will be described in more detail with reference to FIG. 3. An SSis categorized into a PSS and an SSS. The PSS is used to acquiretime-domain synchronization of OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization and theSSS is used to acquire frame synchronization, a cell group ID, and/or CPconfiguration of a cell (i.e. information as to whether a normal CP isused or an extended CP is used). Referring to FIG. 3, each of a PSS andan SSS is transmitted on two OFDM symbols of every radio frame. Morespecifically, SSs are transmitted in the first slot of subframe 0 andthe first slot of subframe 5, in consideration of a global system formobile communication (GSM) frame length of 4.6 ms for facilitation ofinter-radio access technology (inter-RAT) measurement. Especially, a PSSis transmitted on the last OFDM symbol of the first slot of subframe 0and on the last OFDM symbol of the first slot of subframe 5 and an SSSis transmitted on the second to last OFDM symbol of the first slot ofsubframe 0 and on the second to last OFDM symbol of the first slot ofsubframe 5. A boundary of a corresponding radio frame may be detectedthrough the SSS. The PSS is transmitted on the last OFDM symbol of acorresponding slot and the SSS is transmitted on an OFDM symbolimmediately before an OFDM symbol on which the PSS is transmitted. Atransmit diversity scheme of an SS uses only a single antenna port andstandards therefor are not separately defined. That is, a single antennaport transmission scheme or a transmission scheme transparent to a UE(e.g. precoding vector switching (PVS), time switched transmit diversity(TSTD), or cyclic delay diversity (CDD)) may be used for transmitdiversity of an SS.

An SS may represent a total of 504 unique physical layer cell IDs by acombination of 3 PSSs and 168 SSSs. In other words, the physical layercell IDs are divided into 168 physical layer cell ID groups eachincluding three unique IDs so that each physical layer cell ID is a partof only one physical layer cell ID group. Accordingly, a physical layercell ID N^(cell) _(ID) (=3N⁽¹⁾ _(ID)+N⁽²⁾ _(ID)) is uniquely defined asnumber N⁽¹⁾ _(ID) in the range of 0 to 167 indicating a physical layercell ID group and number N⁽²⁾ _(ID) from 0 to 2 indicating the physicallayer ID in the physical layer cell ID group. A UE may be aware of oneof three unique physical layer IDs by detecting the PSS and may be awareof one of 168 physical layer cell IDs associated with the physical layerID by detecting the SSS. A length-63 Zadoff-Chu (ZC) sequence is definedin the frequency domain and is used as the PSS.

Referring to FIG. 3, upon detecting a PSS, a UE may discern that acorresponding subframe is one of subframe 0 and subframe 5 because thePSS is transmitted every 5 ms but the UE cannot discern whether thesubframe is subframe 0 or subframe 5. Accordingly, the UE cannotrecognize the boundary of a radio frame only by the PSS. That is, framesynchronization cannot be acquired only by the PSS. The UE detects theboundary of a radio frame by detecting an SSS which is transmitted twicein one radio frame with different sequences.

Thus, for cell search/re-search, the UE may receive the PSS and the SSSfrom the eNB to establish synchronization with the eNB and acquireinformation such as a cell ID. Thereafter, the UE may receive broadcastinformation in a cell managed by the eNB over a PBCH.

The message content of the PBCH are expressed in a master informationblock (MIB) in a radio resource control (RRC) layer. Specifically, themessage content of the PBCH is shown in Table 3.

TABLE 3   -- ASN1START MasterInformationBlock ::= SEQUENCE { dl-Bandwidth  ENUMERATED {   n6, n15, n25, n50, n75, n100}, phich-Config  PHICH-Config,  systemFrameNumber  BIT STRING (SIZE (8)), spare  BIT STRING (SIZE (10)) } -- ASN1STOP

As shown in Table 4, the MIB includes DL bandwidth (BW), PHICHconfiguration, and a system frame number (SFN). For example, among theparameters of the MIB, the parameter dl-Bandwidth is a parameterindicating the number of RBs N_(RB) on DL. This parameter may indicate aDL system bandwidth in a manner that n6 corresponds to 6 RBs, and n15corresponds to 15 RBs. Among the parameters of the MIB, the parametersytemFrameNumber defines 8 most significant bits of an SFN. The twoleast significant bits of the SFN may be implicitly obtained by decodingthe PBCH. The timing of 40 ms PBCH TTI indicates two least significantbits. For example, in the 40 ms PBCH TTI, the first radio frameindicates 00, the second radio frame indicates 01, the third radio frameindicates 10, and the last radio frame indicates 11. Accordingly, the UEmay be explicitly aware of information about the DL BW, SFN, and PHICHconfiguration by receiving the MIB. Meanwhile, information which may beimplicitly recognized by the UE through reception of the PBCH includesthe number of transmit antenna ports of the eNB. Information about thenumber of transmit antennas of the eNB is implicitly signaled by masking(e.g. XOR operation) a sequence corresponding to the number of transmitantennas to a 16-bit cyclic redundancy check (CRC) used for errordetection of the PBCH. For example, masking sequences shown below may beused according to the number of antennas.

TABLE 4 Number of transmit antenna ports at eNode-B PBCH CRC mask<x_(ant,0), x_(ant,1), . . . , x_(ant,15)> 1 <0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0> 2 <1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1>4 <0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1>

The PBCH is mapped to REs after cell-specific scrambling, modulation,layer mapping, and precoding are applied thereto.

FIG. 3 illustrates exemplary mapping based on one radio frame and, infact, an encoded PBCH is mapped to 4 subframes substantially for 40 ms.The time of 40 ms is blind-detected and explicit signalling about 40 msis not separately present. The PBCH is mapped to 4 OFDM symbols and 72subcarriers in one subframe. The PBCH is not mapped to REs in which RSsfor 4 transmit antennas are located regardless of the number of actualtransmit antennas of the eNB. For reference, even in the frame structureapplied to TDD, illustrated in FIG. 1(b), the PBCH is mapped to 4subframes during 40 ms and is mapped to 4 OFDM symbols and 72subcarriers in one subframe. In TDD, the PBCH may be located on OFDMsymbols 0 to 3 of slot 1 (the rear slot of subframe 0) and slot 11 (therear slot of subframe 5) among slots 0 to 19 of a radio frame.

When a UE accesses an eNB or a cell for the first time or does not havea radio resource allocated for transmission of a signal to the eNB orthe cell, the UE may perform a random access procedure. To perform therandom access procedure, the UE may transmit a specific sequence over aPRACH as a random access preamble, and receive a response message forthe random access preamble over a PDCCH and/or a PDSCH corresponding tothe PDCCH. Thereby, a radio resource necessary for signal transmissionmay be allocated to the UE. In the random access procedure, a UEidentifier may be configured for the UE. For example, a cell radionetwork temporary identifier (C-RNTI) may identify the UE in a cell, andmay be temporary, semi-persistent or permanent. A temporary C-RNTI maybe allocated in a temporary access process, and may become a permanentC-RNTI after contention is resolved. A semi-persistent C-RNTI is used toschedule semi-persistent resources through a PDCCH. The semi-persistentC-RNTI is also called a semi-persistent scheduling (SPS) C-RNTI. Apermanent C-RNTI has a C-RNTI value allocated after contention isresolved in the random access procedure, and is used to schedule adynamic resource.

FIG. 4 illustrates the structure of a DL subframe used in a wirelesscommunication system.

A DL subframe is divided into a control region and a data region in thetime domain. Referring to FIG. 4, a maximum of 3 (or 4) OFDM symbolslocated in a front part of a first slot of a subframe corresponds to thecontrol region. Hereinafter, a resource region for PDCCH transmission ina DL subframe is referred to as a PDCCH region. OFDM symbols other thanthe OFDM symbol(s) used in the control region correspond to the dataregion to which a physical downlink shared channel (PDSCH) is allocated.Hereinafter, a resource region available for PDSCH transmission in theDL subframe is referred to as a PDSCH region. Examples of a DL controlchannel used in 3GPP LTE include a physical control format indicatorchannel (PCFICH), a physical downlink control channel (PDCCH), aphysical hybrid ARQ indicator channel (PHICH), etc. The PCFICH istransmitted in the first OFDM symbol of a subframe and carriesinformation about the number of OFDM symbols available for transmissionof a control channel within a subframe. The PHICH carries a HARQ (HybridAutomatic Repeat Request) ACK/NACK(acknowledgment/negative-acknowledgment) signal as a response to ULtransmission.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a UE or UE group and other controlinformation. Transmit format and resource allocation information of adownlink shared channel (DL-SCH) are referred to as DL schedulinginformation or DL grant. Transmit format and resource allocationinformation of an uplink shared channel (UL-SCH) are referred to as ULscheduling information or UL grant. The size and usage of the DCIcarried by one PDCCH are varied depending on DCI formats. The size ofthe DCI may be varied depending on a coding rate. In the current 3GPPLTE system, various formats are defined, wherein formats 0 and 4 aredefined for a UL, and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 3 and 3A aredefined for a DL. Combination selected from control information such asa hopping flag, RB allocation, modulation coding scheme (MCS),redundancy version (RV), new data indicator (NDI), transmit powercontrol (TPC), cyclic shift, cyclic shift demodulation reference signal(DM RS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI) information istransmitted to the UE as the DCI.

A plurality of PDCCHs may be transmitted within a control region. A UEmay monitor the plurality of PDCCHs. An eNB determines a DCI formatdepending on the DCI to be transmitted to the UE, and attaches cyclicredundancy check (CRC) to the DCI. The CRC is masked (or scrambled) withan identifier (for example, a radio network temporary identifier (RNTI))depending on usage of the PDCCH or owner of the PDCCH. For example, ifthe PDCCH is for a specific UE, the CRC may be masked with an identifier(for example, cell-RNTI (C-RNTI)) of the corresponding UE. If the PDCCHis for a paging message, the CRC may be masked with a paging identifier(for example, paging-RNTI (P-RNTI)). If the PDCCH is for systeminformation (in more detail, system information block (SIB)), the CRCmay be masked with system information RNTI (SI-RNTI). If the PDCCH isfor a random access response, the CRC may be masked with a random accessRNTI (RA-RNTI). For example, CRC masking (or scrambling) includes XORoperation of CRC and RNTI at the bit level.

The PDCCH is transmitted on an aggregation of one or a plurality ofcontinuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide a coding rate based on the status of aradio channel to the PDCCH. The CCE corresponds to a plurality ofresource element groups (REGs). For example, one CCE corresponds to nineresource element groups (REGs), and one REG corresponds to four REs.Four QPSK symbols are mapped to each REG. A resource element (RE)occupied by the reference signal (RS) is not included in the REG.Accordingly, the number of REGs within given OFDM symbols is varieddepending on the presence of the RS. The REGs are also used for otherdownlink control channels (that is, PDFICH and PHICH). The number of DCIformats and DCI bits is determined in accordance with the number ofCCEs. For example, the PCFICH and PHICH include 4 REGs and 3 REGs,respectively. Assuming that the number of REGs not allocated to thePCFICH or the PHICH is N_(REG), the number of available CCEs in a DLsubframe for PDCCH(s) in a system is numbered from 0 to N_(CCE)−1, whereN_(CCE)=floor(N_(REG)/9).

A PDCCH format and the number of DCI bits are determined in accordancewith the number of CCEs. The CCEs are numbered and consecutively used.To simplify the decoding process, a PDCCH having a format including nCCEs may be initiated only on CCEs assigned numbers corresponding tomultiples of n. For example, a PDCCH including n consecutive CCEs may beinitiated only on CCEs satisfying ‘i mod n=0’. Herein, i denotes a CCEindex (or a CCE number).

The number of CCEs used for transmission of a specific PDCCH isdetermined by the eNB in accordance with channel status. For example,one CCE may be required for a PDCCH for a UE (for example, adjacent toeNB) having a good downlink channel. However, in case of a PDCCH for aUE (for example, located near the cell edge) having a poor channel,eight CCEs may be required to obtain sufficient robustness.Additionally, a power level of the PDCCH may be adjusted to correspondto a channel status.

In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH can belocated for each UE is defined. A CCE set in which the UE can detect aPDCCH thereof is referred to as a PDCCH search space or simply as asearch space (SS). An individual resource on which the PDCCH can betransmitted in the SS is called a PDCCH candidate. A set of PDCCHcandidates that the UE is to monitor is defined as the SS. SSs forrespective PDCCH formats may have different sizes and a dedicated SS anda common SS are defined. The dedicated SS is a UE-specific SS (USS) andis configured for each individual UE. The common SS (CSS) is configuredfor a plurality of UEs. The following table shows aggregation levels fordefining SSs.

TABLE 5 Number of PDCCH Search space S_(k) ^((L)) candidates TypeAggregation level L Size [in CCEs] M^((L)) UE- 1 6 6 specific 2 12 6 4 82 8 16 2 Common 4 16 4 8 16 2

The eNB transmits an actual PDCCH (DCI) on a PDCCH candidate in a searchspace and the UE monitors the search space to detect the PDCCH (DCI).Here, monitoring implies attempting to decode each PDCCH in thecorresponding SS according to all monitored DCI formats. The UE maydetect a PDCCH thereof by monitoring a plurality of PDCCHs. Basically,the UE does not know the location at which a PDCCH thereof istransmitted. Therefore, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having an IDthereof is detected and this process is referred to as blind detection(or blind decoding (BD)).

For example, it is assumed that a specific PDCCH is CRC-masked with aradio network temporary identity (RNTI) ‘A’ and information about datatransmitted using a radio resource ‘B’ (e.g. frequency location) andusing transport format information ‘C’ (e.g. transmission block size,modulation scheme, coding information, etc.) is transmitted in aspecific DL subframe. Then, the UE monitors the PDCCH using RNTIinformation thereof. The UE having the RNTI ‘A’ receives the PDCCH andreceives the PDSCH indicated by ‘B’ and ‘C’ through information of thereceived PDCCH.

In order for the receiving device to restore a signal transmitted by thetransmitting device, an RS for estimating a channel between thereceiving device and the transmitting device is needed. RSs may becategorized into RSs for demodulation and RSs for channel measurement.CRSs defined in the 3GPP LTE system can be used for both demodulationand channel measurement. In a 3GPP LTE-A system, a UE-specific RS(hereinafter, a UE-RS) and a CSI-RS are further defined in addition to aCRS. The UE-RS is used to perform demodulation and the CSI-RS is used toderive CSI. Meanwhile, RSs are divided into a dedicated RS (DRS) and acommon RS (CRS) according to whether a UE recognizes presence thereof.The DRS is known only to a specific UE and the CRS is known to all UEs.Among RSs defined in the 3GPP LTE-A system, the cell-specific RS may beconsidered a sort of the common RS and the DRS may be considered a sortof the UE-RS.

For reference, demodulation may be viewed as a part of the decodingprocess. In the present invention, the terms demodulation and decodingare used interchangeably.

FIG. 5 illustrates configuration of cell specific reference signals(CRSs) and user specific reference signals (UE-RS). In particular, FIG.5 shows REs occupied by the CRS(s) and UE-RS(s) on an RB pair of asubframe having a normal CP.

In an existing 3GPP system, since CRSs are used for both demodulationand measurement, the CRSs are transmitted in all DL subframes in a cellsupporting PDSCH transmission and are transmitted through all antennaports configured at an eNB.

A UE may measure CSI using the CRSs and demodulate a signal received ona PDSCH in a subframe including the CRSs. That is, the eNB transmits theCRSs at predetermined locations in each RB of all RBs and the UEperforms channel estimation based on the CRSs and detects the PDSCH. Forexample, the UE may measure a signal received on a CRS RE and detect aPDSCH signal from an RE to which the PDSCH is mapped using the measuredsignal and using the ratio of reception energy per CRS RE to receptionenergy per PDSCH mapped RE. However, when the PDSCH is transmitted basedon the CRSs, since the eNB should transmit the CRSs in all RBs,unnecessary RS overhead occurs. To solve such a problem, in a 3GPP LTE-Asystem, a UE-specific RS (hereinafter, UE-RS) and a CSI-RS are furtherdefined in addition to a CRS. The UE-RS is used for demodulation and theCSI-RS is used to derive CSI. The UE-RS is one type of DRS. Since theUE-RS and the CRS are used for demodulation, the UE-RS and the CRS maybe regarded as demodulation RSs in terms of usage. Since the CSI-RS andthe CRS are used for channel measurement or channel estimation, theCSI-RS and the CRS may be regarded as measurement RSs.

UE-RSs are transmitted on antenna port(s) p=5, p=7, p=8 or p=7, 8, . . ., υ+6 for PDSCH transmission, where υ is the number of layers used forthe PDSCH transmission. UE-RSs are present and are a valid reference forPDSCH demodulation only if the PDSCH transmission is associated with thecorresponding antenna port. UE-RSs are transmitted only on RBs to whichthe corresponding PDSCH is mapped. That is, the UE-RSs are configured tobe transmitted only on RB(s) to which a PDSCH is mapped in a subframe inwhich the PDSCH is scheduled unlike CRSs configured to be transmitted inevery subframe irrespective of whether the PDSCH is present.Accordingly, overhead of the RS may be lowered compared to that of theCRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 7, in a PRB having frequency-domain index n_(PRB)assigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . .. , υ+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols a_(k,l) ^((p)) in a subframe according to thefollowing equation.a _(k,l) ^((p)) =w _(p)(l′)·r(3·l′·N _(RB) ^(max,DL)+3·n _(PRB)+m′)  [Equation 1]where w_(p)(i), l′, m′ are given as follows.

$\begin{matrix}{\mspace{20mu}{{w_{p}(i)} = \{ {{\begin{matrix}{{\overset{\_}{w}}_{p}(i)} & {{( {m^{\prime} + n_{PRB}} ){mod}\; 2} = 0} \\{{\overset{\_}{w}}_{p}( {3 - i} )} & {{( {m^{\prime} + n_{PRB}} ){mod}\; 2} = 1}\end{matrix}\mspace{20mu} k} = {{{5m^{\prime}} + {N_{sc}^{RB}n_{PRB}} + {k^{\prime}\mspace{20mu} k^{\prime}}} = \{ \begin{matrix}1 & {p \in \{ {7,8,11,13} \}} \\0 & {p \in \{ {9,10,12,14} \}}\end{matrix} }} }} & \lbrack {\mspace{14mu} 2} \rbrack \\{l = \{ {{\begin{matrix}{{l^{\prime}{mod}\; 2} + 2} & \begin{matrix}{{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\{{{configuration}\mspace{14mu} 3},4,{{or}\mspace{14mu} 8\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\\begin{matrix}{{l^{\prime}{mod}\; 2} +} \\{2 + {3\lfloor {l^{\prime}/2} \rfloor}}\end{matrix} & \begin{matrix}{{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{{l^{\prime}{mod}\; 2} + 5} & {{if}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}}\end{matrix}l^{\prime}} = \{ \begin{matrix}{0,1,2,3} & \begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{0,1} & \begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{2,3} & \begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix}\end{matrix} } } & \; \\{\mspace{20mu}{{m^{\prime} = 0},1,2}} & \;\end{matrix}$

where n_(s) is the slot number within a radio frame and an integer among0 to 19. The sequence w _(p) (i) for normal CP is given according to thefollowing equation.

TABLE 6 Antenna port p [w _(p)(0) w _(p)(1) w _(p)(2) w _(p)(3)] 7 [+1+1 +1 +1] 8 [+1 −1 +1 −1] 9 [+1 +1 +1 +1] 10 [+1 −1 +1 −1] 11 [+1 +1 −1−1] 12 [−1 −1 +1 +1] 13 [+1 −1 −1 +1] 14 [−1 +1 +1 −1]

For antenna port p∈{7, 8, . . . , υ+6}, the UE-RS sequence r(m) isdefined as follows

$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\;\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = \{ \begin{matrix}{0,1,\ldots\mspace{14mu},{{12N_{RB}^{{{ma}\; x},{DL}}} - 1}} & {{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}} \\{0,1,\ldots\mspace{14mu},{{16N_{RB}^{{{ma}\; x},{DL}}} - 1}} & {{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} }} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

c(i) is a pseudo-random sequence defined by a length-31 Gold sequence.The output sequence c(n) of length M_(PN), where n=0, 1, . . . ,M_(PN)−1, is defined by the following equation.c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  [Equation 4]

where N_(C)=1600 and the first m-sequence is initialized with x₁(0)=1,x₁(n)=0, n=1, 2, . . . , 30. The initialization of the second m-sequenceis denoted by c_(init)=Σ_(i=0) ³⁰x₂(i)·2^(i) with the value depending onthe application of the sequence.

In Equation 3, the pseudo-random sequence generator for generating c(i)is initialized with c_(init) at the start of each subframe according tothe following equation.c _(init)=(└n _(s)/2┘+1)·(2n _(ID) ^((n) ^(SCID) ⁾+1)·2¹⁶ +n_(SCID)  [Equation 5]

In Equation 5, the quantities n^((i)) _(ID), i=0,1, which iscorresponding to n_(ID) ^((n) ^(SCID) ⁾, is given by a physical layercell identifier N^(cell) _(ID) if no value for n^(DMRS,i) _(ID) isprovided by higher layers or if DCI format 1A, 2B or 2C is used for DCIformat associated with the PDSCH transmission, and given by n^(DMRS,i)_(ID) otherwise.

In Equation 5, the value of n_(SCID) is zero unless specified otherwise.For a PDSCH transmission on antenna ports 7 or 8, n_(SCID) is given bythe DCI format 2B or 2D. DCI format 2B is a DCI format for resourceassignment for a PDSCH using a maximum of two antenna ports havingUE-RSs. DCI format 2C is a DCI format for resource assignment for aPDSCH using a maximum of 8 antenna ports having UE-RSs.

In case of DCI format 2B, n_(SCID) is indicated by the scrambling entityfield according to the following table.

TABLE 7 Scrambling identity field in DCI format 2B n_(SCID) 0 0 1 1

In case of DCI format 2C, n_(SCID) is given by the following table.

TABLE 8 One Codeword: Two Codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7, n_(SCID) = 0 0 2 layers, ports 7-8, n_(SCID)= 0 1 1 layer, port 7, n_(SCID) = 1 1 2 layers, ports 7-8, n_(SCID) = 12 1 layer, port 8, n_(SCID) = 0 2 3 layers, ports 7-9 3 1 layer, port 8,n_(SCID) = 1 3 4 layers, ports 7-10 4 2 layers, ports 7-8 4 5 layers,ports 7-11 5 3 layers, ports 7-9 5 6 layers, ports 7-12 6 4 layers,ports 7-10 6 7 layers, ports 7-13 7 Reserved 7 8 layers, ports 7-14

FIG. 6 illustrates the structure of a UL subframe used in a wirelesscommunication system.

Referring to FIG. 6, a UL subframe may be divided into a data region anda control region in the frequency domain. One or several PUCCHs may beallocated to the control region to deliver UCI. One or several PUSCHsmay be allocated to the data region of the UE subframe to carry userdata.

In the UL subframe, subcarriers distant from a direct current (DC)subcarrier are used as the control region. In other words, subcarrierslocated at both ends of a UL transmission BW are allocated to transmitUCI. A DC subcarrier is a component unused for signal transmission andis mapped to a carrier frequency f₀ in a frequency up-conversionprocess. A PUCCH for one UE is allocated to an RB pair belonging toresources operating on one carrier frequency and RBs belonging to the RBpair occupy different subcarriers in two slots. The PUCCH allocated inthis way is expressed by frequency hopping of the RB pair allocated tothe PUCCH over a slot boundary. If frequency hopping is not applied, theRB pair occupies the same subcarriers.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling request (SR): SR is information used to request a        UL-SCH resource and is transmitted using an on-off keying (OOK)        scheme.    -   HARQ-ACK: HARQ-ACK is a response to a PDCCH and/or a response to        a DL data packet (e.g. a codeword) on a PDSCH. HARQ-ACK        indicates whether the PDCCH or PDSCH has been successfully        received. 1-bit HARQ-ACK is transmitted in response to a single        DL codeword and 2-bit HARQ-ACK is transmitted in response to two        DL codewords. A HARQ-ACK response includes a positive ACK        (simply, ACK), negative ACK (NACK), discontinuous transmission        (DTX), or NACK/DRX. HARQ-ACK is used interchangeably with HARQ        ACK/NACK and ACK/NACK.    -   Channel state information (CSI): CSI is feedback information for        a DL channel. CSI may include channel quality information (CQI),        a precoding matrix indicator (PMI), a precoding type indicator,        and/or a rank indicator (RI). In the CSI, MIMO-related feedback        information includes the RI and the PMI. The RI indicates the        number of streams or the number of layers that the UE can        receive through the same time-frequency resource. The PMI is a        value reflecting a space characteristic of a channel, indicating        an index of a preferred precoding matrix for DL signal        transmission based on a metric such as an SINR. The CQI is a        value of channel strength, indicating a received SINR that can        be obtained by the UE generally when the eNB uses the PMI.

If a UE uses a single carrier frequency division multiple access(SC-FDMA) scheme in UL transmission, a PUCCH and a PUSCH cannot besimultaneously transmitted on one carrier in a 3GPP LTE release-8 orrelease-9 system in order to maintain a single carrier property. In a3GPP LTE release-10 system, support/non-support of simultaneoustransmission of the PUCCH and the PUSCH may be indicated by higherlayers.

The present invention may be applied to an EPDCCH and a PUSCH, and aPDSCH and/or PUSCH scheduled by the EPDCCH, as well as a PDCCH and aPUCCH, and a PDSCH and/or PUSCH scheduled by the PDCCH.

FIG. 7 illustrates a physical downlink control channel (PDCCH) or anenhanced PDCCH (EPDCCH), and a data channel scheduled by PDCCH/EPDCCH.Particularly, FIG. 7 illustrates the case in which the EPDCCH isconfigured by spanning the fourth symbol (OFDM symbol #3) to the lastsymbol of a subframe. The EPDCCH may be configured using consecutivefrequency resources or may be configured using discontinuous frequencyresources for frequency diversity.

Referring to FIG. 7, PDCCH 1 and PDCCH 2 may schedule PDSCH 1 and PDSCH2, respectively, and the EPDCCH may schedule another PDSCH. Similarly tothe case of a PDCCH, specific resource assignment units may be definedfor the EPDCCH and the EPDCCH may be configured by a combination of thedefined specific resource assignment units. When the specific resourceassignment units are used, there is an advantage of enabling executionof link adaptation because less resource assignment units can be used toconfigure the EPDCCH in the case of a good channel state and moreresource assignment units can be used to configure the EPDCCH in thecase of a poor channel state. Hereinafter, in order to distinguish abasic unit of the EPDCCH from a CCE which is a basic unit of the PDCCH,the basic unit of the EPDCCH will be referred to as an enhanced CCE(ECCE). It is assumed hereinafter that, for an aggregation level L ofthe EPDCCH, the EPDCCH is transmitted on an aggregation of L ECCEs.Namely, like the aggregation level of the PDCCH, the aggregation levelof the EPDCCH also refers to the number of ECCEs used for transmissionof one DCI. Hereinafter, an aggregation of ECCEs on which the UE iscapable of detecting the EPDCCH thereof will be referred to as an EPDCCHsearch space. DCI carried by the EPDCCH is mapped to a single layer andthen precoded.

The ECCEs constituting the EPDCCH may be categorized into a localizedECCE (hereinafter, L-ECCE) and a distributed ECCE (hereinafter, D-ECCE)according to a scheme of mapping the ECCE(s) to RE(s). The L-CCE meansthat REs constituting an ECCE are extracted from the same PRB pair. Ifthe EPDCCH is configured using L-ECCE(s), beamforming optimized for eachUE can be performed. On the other hand, the D-ECCE corresponds to thecase in which REs constituting the ECCE are extracted from different PRBpairs. Unlike the L-ECCE, the D-ECCE can acquire frequency diversity inspite of a restriction on beamforming. In localized mapping, a singleantenna port p∈{107,108,109,110} used for EPDCCH transmission is afunction of index(es) of the ECCE for defining the EPDCCH. Indistributed mapping, REs in an EREG are associated with one of twoantenna ports in an alternating manner.

Unlike the PDCCH transmitted based on the CRS, the EPDCCH is transmittedbased on the demodulation RS (hereinafter, DM-RS). Accordingly, the UEdecodes/demodulates the PDCCH based on the CRS and decodes/demodulatesthe EPDCCH based on the DM-RS. The DM-RS associated with EPDCCH istransmitted on the same antenna port p∈{107,108,109,110} as theassociated EPDCCH physical resource, is present for EPDCCH demodulationonly if the EPDCCH transmission is associated with the correspondingantenna port, and is transmitted only on the PRB(s) upon which thecorresponding EPDCCH is mapped.

In case of normal CP, for the antenna port p∈{107,108,109,110} in a PRBn_(PRB) assigned for EPDCCH transmission, a part of the DM-RS sequencer(m) can be mapped to complex-modulation symbols a_(k,l) ^((p)) in asubframe according to the following equation.a _(k,l) ^((p)) =w _(p)(l′)·r(3·l′·N _(RB) ^(max,DL)+3·n _(PRB)+m′)  [Equation 6]

where w_(p)(i), l′, m′ can be given by the following equation.

$\begin{matrix}\begin{matrix}{\mspace{20mu}{{w_{p}(i)} = \{ {{\begin{matrix}{{\overset{\_}{w}}_{p}(i)} & {{( {m^{\prime} + n_{PRB}} ){mod}\; 2} = 0} \\{{\overset{\_}{w}}_{p}( {3 - i} )} & {{( {m^{\prime} + n_{PRB}} ){mod}\; 2} = 1}\end{matrix}\mspace{20mu} k} = {{{5m^{\prime}} + {N_{sc}^{RB}n_{PRB}} + {k^{\prime}\mspace{20mu} k^{\prime}}} = \{ \begin{matrix}1 & {p \in \{ {107,108} \}} \\0 & {p \in \{ {109,110} \}}\end{matrix} }} }} \\{l = \{ \begin{matrix}{{l^{\prime}{mod}\; 2} + 2} & \begin{matrix}{{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\{{{configuration}\mspace{14mu} 3},4,{{or}\mspace{14mu} 8\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\\begin{matrix}{{l^{\prime}{mod}\; 2} +} \\{2 + {3\lfloor {l^{\prime}/2} \rfloor}}\end{matrix} & \begin{matrix}{{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{{l^{\prime}{mod}\; 2} + 5} & {{if}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}}\end{matrix} }\end{matrix} & \lbrack {{Equation}\mspace{14mu} 7} \rbrack \\{l^{\prime} = \{ \begin{matrix}{0,1,2,3} & \begin{matrix}\begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{in}\mspace{14mu} a}} \\{{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}\end{matrix} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{0,1} & \begin{matrix}\begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}}} \\{{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}\end{matrix} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix} \\{2,3} & \begin{matrix}\begin{matrix}{{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}}} \\{{special}\mspace{14mu}{subframe}\mspace{14mu}{with}}\end{matrix} \\{{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{14mu}( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} )}}\end{matrix}\end{matrix} } & \; \\{\mspace{20mu}{{m^{\prime} = 0},1,2}} & \;\end{matrix}$

where the sequence w _(p)(i) for normal CP is given by the followingtable.

TABLE 9 Antenna port p [w _(p)(0) w _(p)(1) w _(p)(2) w _(p)(3)] 107 [+1+1 +1 +1] 108 [+1 −1 +1 −1] 109 [+1 +1 +1 +1] 110 [+1 −1 +1 −1]

For example, in FIG. 7, the REs occupied by the UE-RS(s) of the antennaport 7 or 8 may be occupied by the DM-RS(s) of the antenna port 107 or108 on the PRB to which the EPDCCH is mapped, and the REs occupied bythe UE-RS(s) of antenna port 9 or 10 may be occupied by the DM-RS(s) ofthe antenna port 109 or 110 on the PRB to which the EPDCCH is mapped. Inother words, a certain number of REs are used on each RB pair fortransmission of the DM-RS for demodulation of the EPDCCH regardless ofthe UE or cell if the type of EPDCCH and the number of layers are thesame as in the case of the UE-RS for demodulation of the PDSCH.Hereinafter, the PDCCH and the EPDCCH will be simply referred to asPDCCH. Embodiments of the present invention applied to the PDCCH may besimilarly applied to the EPDCCH.

For the antenna port p∈{7, 8, . . . , u+6}, the UE-RS sequence r(m) forthe EPDCCH is defined by Equation 3. The pseudo-random sequence c(i) ofEquation 3 is defined by Equation 4, and the pseudo-random sequencegenerator for generating c(i) is initialized as c_(init) at the start ofeach subframe according to the following equation.c _(init)=(└n _(s)/2┘+1)·(2n _(ID) ^(EPDCCH)+1)·2¹⁶ +n _(SCID)^(EPDCCH)  [Equation 8]

The EPDCCH DMRS scrambling sequence initialization parameter n^(EPDCCH)_(SCID) is provided by a higher layer signal.

FIG. 8 is a block diagram illustrating elements of a transmitting device10 and a receiving device 20 for implementing the present invention.

The transmitting device 10 and the receiving device 20 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedembodiments of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 10 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into N_(layer) layers through demultiplexing, channelcoding, scrambling, and modulation. The coded data stream is alsoreferred to as a codeword and is equivalent to a transport block whichis a data block provided by a MAC layer. One transport block (TB) iscoded into one codeword and each codeword is transmitted to thereceiving device in the form of one or more layers. For frequencyup-conversion, the RF unit 13 may include an oscillator. The RF unit 13may include N_(t) (where N_(t) is a positive integer) transmit antennas.

A signal processing process of the receiving device 20 is the reverse ofthe signal processing process of the transmitting device 10. Undercontrol of the processor 21, the RF unit 23 of the receiving device 20receives radio signals transmitted by the transmitting device 10. The RFunit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 10 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 20. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 20 and enables the receiving device 20 to derivechannel estimation for the antenna, irrespective of whether the channelrepresents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 20 in UL and as the transmitting device 10 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

FIG. 9 illustrates an overview of physical channel processing. Abaseband signal representing a PUSCH or a PDSCH may be defined by aprocessing procedure of FIG. 9.

Referring to FIG. 9, a transmitting device may include scramblers 301,modulation mappers 302, a layer mapper 303, a precoder 304, RE mappers305, and OFDM signal generators 306.

The transmitting device 10 may transmit more than one codeword. Thescramblers 301 scramble the coded bits of each codeword, fortransmission on a physical channel.

The modulation mappers 302 modulate the scrambled bits, thus producingcomplex-valued modulation symbols. The modulation mappers 302 modulatethe scrambled bits to complex-valued modulation symbols representingpositions on a signal constellation in a predetermined modulationscheme. The modulation scheme may be, but not limited to, any of m-phaseshift keying (m-PSK) and m-quadrature amplitude modulation (m-QAM).

The layer mapper 303 maps the complex-valued modulation symbols to oneor several transmission layers.

The precoder 304 may precode the complex-valued modulation symbols oneach layer, for transmission through the antenna ports. Morespecifically, the precoder 304 generates antenna-specific symbols byprocessing the complex-valued modulation symbols for multipletransmission antennas in a MIMO scheme, and distributes theantenna-specific symbols to the RE mappers 305. That is, the precoder304 maps the transmission layers to the antenna ports. The precoder 304may multiply an output x of the layer mapper 303 by an N_(t)×M_(t)precoding matrix W and output the resulting product in the form of anN_(t)×M_(F) matrix z. Here, N_(t) is corresponding to the number oftransmission antennas, and M_(t) is corresponding the number of layers.Since the precoder 304 is differently configured according to theprecoding matrix, if the same precoding matrix is applied to signals,this indicates that the same precoder is applied to signals in thepresent invention and if different precoding matrices are applied tosignals, this indicates that different precoders are applied to signalsin the present invention.

The RE mappers 305 map/allocate the complex-valued modulation symbolsfor the respective antenna ports to REs. The RE mappers 305 may allocatethe complex-valued modulation symbols for the respective antenna portsto appropriate subcarriers, and may multiplex them according to UEs.

The OFDM signal generators 306 modulate the complex-valued modulationsymbols for the respective antenna ports, that is, the antenna-specificsymbols through OFDM or SC-FDM modulation, thereby producing acomplex-valued time domain orthogonal frequency division multiplexing(OFDM) or single carrier frequency division multiplexing (SC-FDM) symbolsignal. The OFDM signal generators 306 may perform inverse fast Fouriertransform (IFFT) on the antenna-specific symbols and insert a cyclicprefix (CP) into the resulting IFFT time domain symbol.Digital-to-analog conversion, frequency upconversion, etc applied to theOFDM symbol and then transmitted through the transmission antennas to areceiving device 20. The OFDM signal generators 306 may include an IFFTmodule, a CP inserter, a digital-to-analog converter (DAC), a frequencyupconverter, etc.

In the meantime, if the UE or eNB applies the SC-FDMA scheme to codewordtransmission, the transmitter or processor may include a discreteFourier transform (DFT) module 307 (or fast Fourier transform (FFT)module). The DFT module 307 performs DFT or FFT (hereinafter referred toas DFT/FFT) on the antenna specific symbol, and outputs the DFT/FFTsymbol to the resource element mapper 305.

The receiving device 20 operates in the reverse order to the operationof the transmitting device 10. Specifically, the receiving device mayinclude a signal recoverer for recovering a received signal into abaseband signal, a multiplexer for multiplexing a received and processedsignal, and a channel demodulator for demodulating a multiplexed signalstream into a codeword. The signal recoverer, the multiplexer, and thechannel demodulator may be comprised of one integrated module orindependent modules for performing respective functions. For example,the signal recoverer may include an analog-to-digital converter (ADC)for converting an analog signal into a digital signal, a CP remover forremoving a CP from the digital signal, an FFT module for generating afrequency-domain symbol by performing FFT upon the CP-removed signal,and an RE demapper/equalizer for recovering the frequency-domain symbolinto an antenna-specific symbol. The multiplexer recovers theantenna-specific symbol into a transmission layer and the channeldemodulator recovers the transmission layer into the codeword that thetransmitting device desires to transmit.

Meanwhile, upon receiving signals transmitted by an SC-FDMA scheme, thereceiving device 20 further includes an inverse discrete Fouriertransmission (IFFT) module (or an inverse fast Fourier transform (IFFT)module). The IDFT/IFFT module performs IDFT/IFFT upon theantenna-specific symbols recovered by the RE demapper and transmits theIDFT/IFFT-processed symbol to the multiplexer.

For reference, the processor 11 of the transmitting device 10 may beconfigured to include the scramblers 301, the modulation mappers 302,the layer mapper 303, the precoder 304, the RE mappers 305, and the OFDMsignal generators 306. Likewise, the processor 21 of the receivingdevice 20 may be configured to include the signal recoverer, themultiplexer, and the channel demodulator.

Recently, machine type communication (MTC) has come to the fore as asignificant communication standard issue. MTC refers to exchange ofinformation between a machine and an eNB without involving persons orwith minimal human intervention. For example, MTC may be used for datacommunication for measurement/sensing/reporting such as meter reading,water level measurement, use of a surveillance camera, inventoryreporting of a vending machine, etc. and may also be used for automaticapplication or firmware update processes for a plurality of UEs. In MTC,the amount of transmission data is small and UL/DL data transmission orreception (hereinafter, transmission/reception) occurs occasionally. Inconsideration of such properties of MTC, it would be better in terms ofefficiency to reduce production cost and battery consumption of UEs forMTC (hereinafter, MTC UEs) according to data transmission rate. Sincethe MTC UE has low mobility, the channel environment thereof remainssubstantially the same. If an MTC UE is used for metering, reading of ameter, surveillance, and the like, the MTC UE is very likely to belocated in a place such as a basement, a warehouse, and mountain regionswhich the coverage of a typical eNB does not reach. In consideration ofthe purposes of the MTC UE, it is better for a signal for the MTC UE tohave wider coverage than the signal for the conventional UE(hereinafter, a legacy UE).

When considering the usage of the MTC UE, there is a high probabilitythat the MTC UE requires a signal of wide coverage compared with thelegacy UE. Therefore, if the eNB transmits a PDCCH, a PDSCH, etc. to theMTC UE using the same scheme as a scheme of transmitting the PDCCH, thePDSCH, etc. to the legacy UE, the MTC UE has difficulty in receiving thePDCCH, the PDSCH, etc. Therefore, the present invention proposes thatthe eNB apply a coverage enhancement scheme such as subframe repetition(repetition of a subframe with a signal) or subframe bundling upontransmission of a signal to the MTC UE having a coverage issue so thatthe MTC UE can effectively receive a signal transmitted by the eNB. Forexample, the PDCCH and PDSCH may be transmitted to the MTC UE having thecoverage issue in a plurality of subframes (e.g. about 100 subframes).In this case, if the PDSCH is transmitted in a subframe in which thePDCCH is transmitted, the UE is problematic in that the PDSCH for allsubframes in which the PDCCH is transmitted should be buffered until theUE has successfully received the PDCCH. Further, if the PDCCH istransmitted in each of multiple subframes and the UE has successfullyreceived the PDCCH using the multiple subframes, the UE has a problemwith uncertainty about a subframe in which transmission of the PDCCHcarrying the same DCI is started. The present invention proposes methodsfor solving problems which may be generated in the process oftransmitting a signal to the MTE UE having the coverage issue. Sinceembodiments of the present invention described hereinbelow are methodsfor coverage enhancement, the present invention may be applied not onlyto the MTC UE but also to other UEs having the coverage issue.Accordingly, the embodiments of the present invention may be applied toa UE operating in a coverage enhancement mode. For convenience ofdescription, a UE configured to implement a coverage enhancement methodaccording to the present invention is referred to as the MTC UE and a UEthat is not configured to implement the coverage enhancement methodaccording to the present invention is referred to as the legacy UE.

Hereinafter, a set of subframes in which the receiving device 20 canperform signal transmission used for decoding through combinations ofsignals will be referred to as a subframe bundle. For example, a set ofsubframes in which PDCCHs carrying the same DCI can be transmitted maybe a subframe bundle for PDCCH transmission. In addition,PDCCHs/PDSCHs/PBCHs/PUCCHs/PUSCHs transmitted in multiple subframes tocarry the same data/information/content are respectively referred to asa PDCCH/PDSCH/PBCH/PUCCH/PUSCH bundle. In addition, subframes in whichPDCCH/PDSCH/PBCH/PUCCH/PUSCH bundle transmission can be performed areparticularly referred to as a PDCCH/PDSCH/PBCH/PUCCH/PUSCH subframebundle. In a legacy LTE/LTE-A system, physical channels transmittedrespectively in consecutive (DL or UL) subframes are individuallydecoded, rather than being decoded together and restored into one pieceof information/data. In contrast, in PDCCH/PDSCH/PBCH/PUCCH/PUSCH bundletransmission according to the present invention, physical channels ofmultiple subframes in a corresponding bundle carryinformation/data/content that are identical or can be combined.Accordingly, the UE according to the present invention may decode aphysical channel received in one subframe belonging to a subframe bundleor use physical channels received repeatedly in multiple subframes inthe subframe bundle for decoding. A maximum number of repetitivetransmissions or receptions of a physical channel by the UE maycorrespond to the size of the subframe bundle.

<A. PDCCH Over Subframes>

Transmission of a PDCCH

FIG. 10 illustrates a signal transmission/reception method according toembodiment A of the present invention.

A PDCCH for an MTC UE may be repeatedly transmitted over numeroussubframes for coverage enhancement. The UE may repeatedly receive thePDCCH in a subframe bundle in which multiple subframes are bundled andsuccessfully receive the PDCCH using repeatedly received PDCCH signalsin the multiple subframes. For example, as illustrated in FIG. 10(a),the PDCCH may be repeatedly transmitted over a bundle of N subframes.The UE may successfully receive the PDCCH using n (1≤n≤N) subframesamong the N subframes.

The number, N, of subframes included in a subframe bundle in which thePDCCH is transmitted may always have a cell-specific value. Therefore,both the size of a subframe bundle for PDCCH transmission forcell-specific data transmission such as an SIB etc. or the size of asubframe bundle for PDCCH transmission for UE-specific data transmissionmay be cell-specific. In this case, the size N of the subframe bundle inwhich the PDCCH is transmitted may be a predefined fixed value.Alternatively, the size N of the subframe in which the PDCCH istransmitted may be a value configured for the UE through an MIB or anSIB. Such a PDCCH transmission subframe bundle may consist ofnon-consecutive subframes as well as consecutive subframes.

The size N of the subframe bundle in which the PDCCH is transmitted maybe a cell-specific value for PDCCH transmission to transmitcell-specific data such as an SIB or may be a UE-specific value forPDCCH transmission to transmit UE-specific data. The size N of thesubframe bundle in which the PDCCH is UE-specifically transmitted may beconfigured for the UE through a higher layer signal such as an RRCsignal. Alternatively, the size N of the subframe bundle may bepre-fixed and pre-stored in the eNB and the UE.

In order for the UE to receive the PDCCH many times through a subframebundle consisting of multiple subframes, the UE should be aware of astart location of a subframe with the PDCCH. A PDCCH of the legacyLTE/LTE-system may be transmitted in every DL subframe as illustrated inFIG. 4. Accordingly, the PDCCH in the legacy LTE/LTE-A system may betransmitted in an arbitrary DL subframe whenever the eNB requires thePDCCH and the UE attempts to decode the PDCCH in every DL subframe underthe assumption that the PDCCH can be received in every DL subframe. Incontrast, according to the present invention, transmission of the PDCCHis started only in a prescheduled subframe, not in an arbitrarysubframe. Alternatively, such a transmission start subframe location ofa PDCCH bundle may be defined as a fixed value. The fixed value may alsobe transmitted through an MIB. For example, if it is assumed thattransmission of the PDCCH bundle is started only in a subframe having anSFN satisfying ‘SFN % N=0’ (where % denotes a modulo operator), thevalue N may be transmitted through the MIB. If it is assumed thattransmission of the PDCCH bundle is started only in a subframe having anSFN satisfying ‘SFN % N=offset’, the offset value may be transmittedthrough the MIB. As an example, if PDCCH transmission for an MTC UE witha coverage issue is started only in subframes (subframe #0, #100, #200,#300, . . . ), the UE may attempt to receive the PDCCH in N subframesstarting from a subframe with an SFN corresponding to a multiple of 100.Characteristically, a subframe location at which transmission of a PDCCHbundle may be started may be UE-specific. In this case, informationabout the subframe location at which transmission of the PDCCH bundlemay be started may be pre-configured through a higher layer signal suchas an RRC signal. The UE may attempt to receive and/or decode acorresponding PDCCH during N subframes starting from a transmissionstart subframe of the PDCCH bundle based on the information (e.g. offsetand/or N) about the transmission start subframe location of the PDCCHbundle. If the PDCCH carries a DL grant, the UE may attempt to receiveand/or decode a PDSCH according to the DL grant in subframe(s) for PDSCHtransmission according to the present invention. If the PDCCH carries aUL grant, the UE may attempt to transmit and/or decode a PUSCH accordingto the UL grant in subframe(s) for PUSCH transmission according to thepresent invention.

If the PDCCH is transmitted over a bundle of multiple subframes, thePDCCH may be transmitted through all or some subframes during a PDCCHtransmission duration as illustrated in FIG. 10(b). In this case, thepresent invention proposes restricting a UE-specific search space or atransmission resource of the PDCCH transmitted starting from a PDCCHtransmission start subframe to a PDCCH transmission end subframe.

A set of PDCCH candidates that the UE is to monitor is defined in theplane of search spaces (SSs) and one SS S^((L)) _(k) at an aggregationlevel L∈{1,2,4,8} is defined by the set of PDCCH candidates. For eachserving cell on which a PDCCH is monitored, the CCEs corresponding toPDCCH candidate m of the search space S^((L)) _(k) are given by thefollowing equation.L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 9]

where Y_(k) may be defined by Equation 12, i=0, . . . , L−1. For thecommon search space, m′=m. For the UE SS, for the serving cell on whichthe PDCCH is monitored, if a carrier indicator field is configured for amonitoring UE, for example, if the UE is informed that the carrierindicator field is present on the PDCCH by a higher layer, thenm′=m+M^((L))·n_(CI) where n_(CI) is a carrier indicator field value. Thecarrier indicator field value is the same as a serving cell index(ServCellIndex) of a corresponding serving cell. The serving cell indexis a short ID used to identify a serving cell and, for example, any oneof integers from 0 to ‘maximum number of carrier frequencies which canbe configured for the UE at a time minus 1’ may be allocated to oneserving cell as the serving cell index. That is, the serving cell indexmay be a logical index used to identify a specific serving cell amongcells allocated to the UE rather than a physical index used to identifya specific carrier frequency among all carrier frequencies. In themeantime, if the UE is not configured with carrier indicator field (CIF)then m′=m, where m′=0, . . . , M^((L))−1. M^((L)) is the number of PDCCHcandidates to monitor in the given search space. Namely, the UE isconfigured to confirm M^((L))(≥L) consecutive CCE(s) or CCE(s) deployedby a specific rule in order to determine whether a PDCCH consisting of LCCEs is transmitted thereto. For reference, the CIF is included in DCIand, in carrier aggregation, the CIF is used to indicate for which cellthe DCI carries scheduling information. An eNB may inform the UE ofwhether the DCI received by the UE may include the CIF through a higherlayer signal. That is, the UE may be configured with the CIF by a higherlayer. Carrier aggregation is described later in more detail.

For the common SSs, Y_(k) is set to 0 for aggregation levels L=4 andL=8. For the UE-specific SS (UE SS) S^((L)) _(k) at aggregation level L,the variable Y_(k) is defined by the following equation.Y _(k)=(A·Y _(k−1))mod D  [Equation 10]

where Y⁻¹=n_(RNTI), A=39827, D=65537 and k=└n_(s)/2┘, n_(s) is the slotnumber within a radio frame. SI-RNTI, C-RNTI, P-RNTI, RA-RNTI, etc. maybe used as an RNTI for n_(RNTI).

When the PDCCH is transmitted through a bundle of multiple subframesaccording to the present invention, if the PDCCH can be transmittedthrough a different PDCCH resource in every subframe, complexity of theUE for receiving the PDCCH is geometrically increased as the number ofPDCCH transmission subframes is increased. In other words, if an SSvaries according to subframes used for PDCCH bundle transmission,complexity of the UE is increased according to the size of a subframebundle. Therefore, the present invention proposes that the PDCCH betransmitted according to any one of the following methods when the PDCCHis transmitted through the subframe bundle.

(1) If the eNB transmits the PDCCH through multiple subframes (i.e. ineach of the multiple subframes) to the UE during a PDCCH transmissionduration, the eNB may transmit the PDCCH through CCE resources using thesame value of m (where m=0, . . . , M^((L))−1) through either a CSS or aUSS during the PDCCH transmission duration. That is, the UE may assumethat the PDCCH is transmitted through a USS resource or a CSS resourcecorresponding to the same value of m during subframes in which the samePDCCH is transmitted.

(2) When the eNB transmits a PDCCH through multiple subframes to the UEduring a PDCCH transmission duration, the eNB may transmit the PDCCHusing CCE(s) corresponding to m=0 through either the CSS or the USSduring the PDCCH transmission duration. That is, the UE may assume thatthe PDCCH is transmitted through a USS resource or a CSS resourcecorresponding to m=0 during subframes with the PDCCH carrying the sameinformation/data/content.

(3) If the eNB transmits a UE-specific PDCCH through multiple subframesto the UE during a PDCCH transmission duration, the eNB may transmit thePDCCH through the same CCE (or EREG or RE) resource during the PDCCHtransmission duration. If the eNB transmits the UE-specific PDCCHthrough the same CCE (or EREG or RE) resource during the PDCCHtransmission duration, the UE may assume that the CCE (or EREG or RE)resource on which the UE-specific PDCCH is transmitted is the same as aCCE (or EREG or RE) resource transmitted in a PDCCH transmission startsubframe.

(3-1) A CCE (or EREG or RE) resource constituting a UE-specific SS,through which the UE-specific PDCCH may be transmitted during the PDCCHtransmission duration may be configured identically to a CCE (or EREG orRE) resource applied to the PDCCH transmission start subframe. The CCE(or EREG or RE) resource applied to the PDCCH transmission startsubframe may be obtained by Equation 9 in the same manner as aconventional scheme.

(3-2) Alternatively, the CCE (or EREG or RE) resource constituting theUE-specific SS, through which the UE-specific PDCCH may be transmittedduring the PDCCH transmission duration may be obtained by Equation 9 andY_(k) may be fixedly used as a specific value other than 0.

Transmission of PDSCH/PUSCH

For an MTC UE with a coverage issue, a PDSCH/PUSCH may also betransmitted through a bundle of multiple subframes. As an example, thePDSCH may be transmitted through D subframes and the UE may successfullyreceive the PDSCH using d (1≤d≤D) subframes among the D PDSCH subframes.Alternatively, for example, the UE may transmit the PUSCH in Dsubframes. The subframe bundle for PDSCH/PUSCH transmission may consistof non-consecutive subframes as well as consecutive subframes.

According to the current LTE standard, the UE may decode a PDCCH andthen decode a PDSCH (except for an SPS PDSCH) according to DCI carriedby the PDCCH in the same subframe with the PDCCH. For the MTC UE withthe coverage issue, since both the PDCCH and the PDSCH can betransmitted over multiple subframes, when the PDSCH should be receivedafter the PDCCH is received may need to be newly defined. Similarly tolegacy transmission of the PDCCH and the PDSCH, a PDCCH carrying a DLgrant for a PDSCH and the PDSCH may be transmitted to the UE in the samesubframe. In this case, since the UE cannot receive a PDSCH associatedwith the PDCCH until the PDCCH is successfully received, there is aproblem in that all PDSCHs received until the UE successively receivesthe PDCCH should be stored. In the case of the MTC UE, some latency ofdata transmission is permitted but it is important to reducemanufacturing costs of the MTC UE. The present invention proposes atransmission scheme as illustrated in FIG. 11 in consideration of thesecharacteristics of the MTC UE.

FIG. 11 illustrates another signal transmission/reception methodaccording to embodiment A of the present invention.

Referring to FIG. 11(a), the eNB may transmit a PDCCH using a bundle ofa total N subframes to the UE. In this case, a PDSCH/PUSCH associatedwith the PDCCH may be transmitted starting from a subframe which followsG subframes after the entire PDCCH bundle is transmitted. That is, forexample, when the last PDCCH is transmitted in subframe N−1, the UE mayassume that the PDSCH/PUSCH is transmitted in a bundle of D subframesstarting from subframe N+G. Although the values N and D may be set todifferent values, they may also be set to the same value. If it isdefined that N=D is always satisfied, the value D may not be indicatedto the UE. The values N and D may be differently or identically set andinformation about the value D may be included in the PDCCH and thentransmitted.

The value G corresponding to a subframe spacing between a PDCCH subframebundle and a PDSCH/PUSCH subframe bundle may be fixed to an invariantspecific value or may be configured for the UE through a higher layersignal such as an MID, an SIB, or a higher layer signal such as an RRCsignal. The value G corresponding to the subframe spacing between thePDCCH subframe bundle and the PDSCH subframe bundle may be fixed to 0.That is, transmission of the PDSCH/PUSCH subframe bundle may beimmediately performed starting from the next subframe after transmissionof the PDCCH subframe bundle is terminated. In addition, the value Gcorresponding to the subframe spacing between the PDCCH subframe bundleand the PUSCH subframe bundle may be fixed to 4. Alternatively, thevalue G corresponding to the subframe spacing between the PDCCH subframebundle and the PUSCH subframe bundle may be fixed to the same value(e.g. G=k_(PUSCH)) as a value when the subframe bundle for the PDCCH isnot configured. For example, k_(PUSCH) may be 4 for FDD and k_(PUSCH)per TDD DL-UL configuration for TDD may be given as follows.

TABLE 10 TDD UL-DL DL subframe number n configuration 0 1 2 3 4 5 6 7 89 0 4 6 4 6 1 6 4 6 4 2 4 4 3 4 4 4 4 6 6 4 4 5 6 4 6 7 7 7 7

In Table 10, a number defined for a DL subframe number n per DL-ULconfiguration may be k_(PUSCH). For example, G3 may be defined dependingupon which subframe number corresponds to the last subframe of the PDCCHsubframe bundle in one radio frame.

If the location of a subframe at which the PDSCH/PUSCH subframe bundleshould be started after the PDCCH subframe bundle is ended is a subframein which the PDSCH/PUSCH cannot be transmitted, the PDSCH/PUSCH bundlemay be started in a subframe which can be used fastest for transmissionof the PDSCH/PUSCH among subframes after the subframe in which thePDSCH/PUSCH cannot be transmitted. In other words, if a subframe N+G isnot an available subframe for PDSCH/PUSCH transmission, the UE mayassume that transmission of the PDSCH/PUSCH bundle is started in asubframe which is available for PDSCH/PUSCH transmission and is nearestthe subframe N+G among subframes after the subframe N+G. Even if thestart subframe of PDSCH/PUSCH bundle transmission is changed, the size Dof the PDSCH/PUSCH bundle may be kept unchanged.

As another method in which the UE can be aware of subframe(s) with aPDSCH/PUSCH indicated by a PDCCH after receiving the PDCCH, the UE mayassume that transmission of a PDSCH/PUSCH bundle is started after apredetermined time since transmission of a PDCCH bundle has beenstarted. Assuming that the difference between a subframe location atwhich transmission of the PDCCH bundle is started and a subframelocation at which transmission of the PDSCH/PUSCH bundle is started is K(e.g. K=100, 200, . . . ) subframes, the UE needs to be aware of inwhich subframe transmission of the PDCCH is started. For example, if itis defined that K=‘PDSCH/PUSCH start subframe index−PDCCH start subframeindex’, the UE may be successfully aware of a timing at which thePDSCH/PUSCH is started only when the UE is aware of a timing at whichthe PDCCH is started. Generally, although the UE will be aware of atransmission start timing of the PDSCH/PUSCH only when the UE is awareof a PDCCH transmission duration N, the above case has an advantage thatthe UE can be aware of a subframe location at which transmission of thePDSCH is started even if the UE is not accurately aware of the PDCCHtransmission duration N. For example, assuming that the eNB transmitsthe PDCCH a maximum of N times wherein an actual number of transmissiontimes of the PDCCH may differ according to determination of the eNB at acorresponding transmission timing, the UE does not know a transmissionend location of the PDCCH but can know a transmission start location ofthe PDSCH. The value K may be fixed or may be configured for the UEthrough an MID, an SIG, or a higher layer signal such as an RRC signal.The value K may be configured to always be the same as the number ofPDCCH subframe bundles. Namely, the PDSCH/PUSCH subframe bundle may beimmediately transmitted starting from the next subframe aftertransmission of the PDCCH subframe bundle is ended. Alternatively, whenthe PDCCH bundle consists of N subframes, the difference K between asubframe location at which the PDCCH bundle is started and a subframelocation at which the PDSCH/PUSCH bundle is started may be fixed to N−1wherein transmission of the PDSCH/PUSCH subframe bundle may be startedin a subframe in which transmission of the PDCCH subframe bundle isended.

When a UE-specific PDCCH bundle is received or a PDCCH bundle isreceived through a USS, if a start subframe of the PDCCH bundle is 0 inFIG. 11(b), information about ACK/NACK for reception of a PDCCH(hereinafter, PDCCH A/N) may be transmitted to the eNB using a ULresource in subframe N+G1 after the next GI subframes of subframe N−1 inwhich the PDCCH bundle is ended. Referring to FIG. 11(b), G1 may be 4and the PDCCH A/N may be transmitted in a bundle of A UL subframes. IfPDCCH A/N information indicates ACK, the eNB that has received the PDCCHA/N information from the UE may transmit a PDSCH in a bundle of Dsubframes starting from subframe N+G1+A+G2 which follows G2 subframesafter receiving the PDCCH A/N in a bundle of subframes N+G1 to N+G+A−1with the PDCCH A/N. After receiving the entire PDSCH bundle, the UE maytransmit A/N information for the PDSCH through a bundle of A2 ULsubframes starting from subframe N+G1+A+G2+G3 which follows G3 subframesstarting from the next subframe of subframe N+G1+A+G2−1 in which thePDSCH bundle is ended. Alternatively, the UE may receive the A/Ninformation for the PUSCH through a bundle of A2 UL subframes startingfrom subframe N+G1+A+G2+G3 which follows G3 subframes after transmittingthe entire PUSCH bundle to the eNB.

The values G1, G2, G3, A, and A2 may be fixed or may be configured forthe UE through an MID, an SIG, or a higher layer signal such as an RRCsignal. Characteristically, the values N, D, A, and A2 may beidentically configured. The value G2 may be 4. The value G3 may be 4 ormay be the same value as a value when subframe bundling for thePDSCH/PUSCH is not configured. For A/N for the PDSCH, G3 may be 4 forFDD. An A/N signal transmitted in UL subframe n in TDD corresponds toPDCCH(s) and a DL SPS release PDCCH detected by the UE in DL subframe(s)n−k (k∈K) where K is given by a UL-DL configuration. The following tableshows K: {k₀, k₁, . . . , k_(M−1)} defined in 3GPP LTE(-A) TDD.

TABLE 11 DL-UL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4— — 6 — 4 1 — — 7,6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, — —4, 6 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, — — — —— — 4, 7 5 — — 13, 12, 9, 8, — — — — — — — 7, 5, 4, 11, 6 6 — — 7 7 5 —— — 7 —

In Table 11, a number defined for subframe n per DL-UL configuration maybe associated with k. For example, G3 may be determined depending uponwhich subframe number corresponds to the last subframe of the PDSCHsubframe bundle. For A/N for the PUSCH, G3 may be 4 in FDD and may begiven as k_(PHICH) in TDD. The following table shows k_(PHICH) per TDDDL-UL configuration.

TABLE 12 TDD UL-DL UL subframe number n configuration 0 1 2 3 4 5 6 7 89 0 4 7 6 4 7 6 1 4 6 4 6 2 6 6 3 6 6 6 4 6 6 5 6 6 4 6 6 4 7

In Table 12, a number defined for UL subframe number n per DL-ULconfiguration may be used as k_(PHICH). For example, G3 may bedetermined depending upon which subframe number corresponds to the lastsubframe of the PUSCH subframe bundle in one radio frame.

FIG. 12 illustrates still another signal transmission/reception methodaccording to embodiment A of the present invention.

As another method in which an MTC UE with a coverage issue transmits aPDSCH may be as follows. For the MTC UE with the coverage issue,transmission of a PDCCH performed through a bundle of multiple subframesmay be started only at a prescheduled subframe location. In this case, aPDSCH bundle transmitted according to a grant through the PDCCH may besimultaneously started in a subframe in which transmission of the PDCCHis started as illustrated in FIG. 12(a).

A special subframe (e.g. special subframe configuration 0 or 5) in whichthe PDSCH cannot be transmitted in TDD mode may be included in asubframe duration during which the PDCCH and the PDSCH should betransmitted. In this case, the following method may be used fortransmission of the PDCCH and the PDSCH. First, if it is assumed thatthe PDCCH should be transmitted through a bundle of N subframes and thePDSCH should be transmitted through a bundle of D subframes, the PDCCHmay be transmitted in each of N subframes for PDCCH bundle transmissionas illustrated in FIG. 12(b). The PDSCH may be transmitted in each of Dsubframes in which the PDSCH can be transmitted except for a subframe(e.g. special subframe) in which the PDSCH cannot be transmitted. Inother words, the number D of subframes for PDSCH bundle transmission maybe counted except for the special subframe. Alternatively, the number Dof subframes for PDSCH bundle transmission including the specialsubframe may be counted wherein the UE may decode the PDSCH by combiningsignals after puncturing a signal of the special subframe, i.e. exceptfor the signal received in the special subframe. This method may beapplied not to all special subframes but to special subframes (e.g.corresponding to special subframe configuration 0 or 5).

<B. No PDCCH Transmission>

FIG. 13 illustrates a signal transmission/reception method according toembodiment B of the present invention.

When repetitive transmission of a PDCCH is performed in order totransmit the PDCCH to an MTC UE with a coverage issue, transmissiondelay and energy consumption for receiving the PDCCH are remarkablyincreased. To solve this problem, the present invention proposes thatthe MTC UE with the coverage issue directly receive a PDSCH withoutreceiving the PDCCH. Alternatively, the present invention proposes thatthe MTC UE with the coverage issue directly transmit a PUSCH withoutreceiving the PDCCH. To this end, the MTC UE with the coverage issue mayreceive the PDSCH transmitted thereto or transmit the PUSCH through adetermined specific resource region.

Subframes in which the PDSCH is transmitted for the MTC UE with thecoverage issue may be reserved by a PDSCH bundle transmission period, aPDSCH bundle transmission offset, and a PDSCH bundle size ‘D’ asillustrated in FIG. 13. The UE may be additionally aware of an RBresource or region in which the PDSCH is transmitted in a subframe.

Referring to FIG. 13, the PDSCH bundle transmission period may indicatea period during which PDSCH bundle transmission is applied, i.e. aperiod during which bundled subframes are configured for PDSCHtransmission. The bundled subframes refer to a bundle of multiplesubframes used for transmission of the same signal/data. The bundledsubframes for bundle transmission may be applied only once or may berepeatedly applied every a predetermined number of frames/subframes.Accordingly, subframes may be bundled only once for PDSCH bundletransmission or PDSCH bundle transmission may be performed in subframesfor PDSCH bundle transmission at every PDSCH bundle transmission period.

The PDSCH bundle transmission offset may indicate a location at whichbundled subframes are started for PDSCH transmission. For example, thePDSCH bundle transmission offset may be information indicating asubframe in which PDSCH bundle transmission is started among subframesin a predetermined number of radio frames or subframes belonging to thePDSCH bundle period. The PDSCH bundle size ‘D’ may correspond to thenumber of bundled subframes among subframes belonging to one PDSCHbundle transmission period. If it is assumed that consecutive DLsubframes are bundled, subframes for PDSCH transmission may be indicatedby the PDSCH bundle transmission offset and the PDSCH bundle size.Instead of the PDSCH bundle transmission offset and PDSCH bundle size, abitmap consisting of bits corresponding one to one to subframes of apredetermined duration or a PDSCH bundle period may be used to reservesubframes for repetitive PDSCH transmission.

Each element for defining a PDSCH/PUSCH for the MTC UE with the coverageissue may be cell-specific or UE-specific. In the case of a transmissionresource of the cell-specific PDSCH/PUSCH, a fixed resource may bepredefined as a transmission resource for PDSCH/PUSCH bundletransmission or may be configured for the UE through an MIB, an SIB, ora higher layer signal such as an RRC signal. A transmission resource ofthe UE-specific PDSCH/PUSCH may be configured for the UE through ahigher layer signal such as an RRC signal. Even in the case of theUE-specific PDSCH/PUSCH resource, the same PDSCH/PUSCH resource may beconfigured for two or more UEs. For example, in order to configure aPDSCH resource region for the MTC UE with the coverage issue, a value ofthe PDSCH bundle transmission period may be cell-specifically configuredand may be configured for the UE through an MIB, an SIB, or a higherlayer signal such as an RRC signal. The PDSCH bundle transmissionoffset, the PDSCH bundle size ‘D’, and an RB region in which the PDSCHis transmitted in a subframe may be UE-specifically configured and maybe configured for the UE through a higher layer signal such as an RRCsignal. The bundle transmission offset value may be designated inassociation with an ID of the UE (e.g. C-RNTI). For example, if the UEis aware of the UE ID thereof (e.g. C-RNTI), the UE may estimate thebundle transmission offset value using the UE ID.

A PDSCH region for cell-specific data transmission, such as an SIB, maybe cell-specifically designated. A PDSCH resource region for UE-specificdata transmission such as data transmission for a specific UE may becell-specifically designated or UE-specifically designated. Uponreceiving cell-specific data through the cell-specific PDSCH resourceregion, the UE may use an SI-RNTI for the MTC UE with the coverage issue(hereinafter, MTC-SI-RNTI). The MTC-SI-RNTI may be predefined as aspecific value among values which are not used for other RNTIs accordingto standard technology. Alternatively, the eNB may inform the UE of theMTC-SI-RNTI included in an MIB.

Alternatively, upon receiving the UE-specific data through thecell-specific or UE-specific PDSCH resource region, the UE may use theC-RNTI. For example, the MTC-SI-RNTI or the C-RNTI may be used in thefollowing processes.

1) Scrambling of bits in a transmission block or code block of acorresponding PDSCH

2) Attachment of a CRC to a transmission block or code block of acorresponding PDSCH

3) Scrambling of a pseudo-random sequence for generation of a UE-RStransmitted through the RB region of a corresponding PDSCH

Regarding Procedure 1), referring to FIG. 9, bits in each codewordtransmitted on a physical channel in one subframe are scrambled prior tomodulation 302. The block of bits b^((q))(0), . . . , b^((q))(M_(bit)^((q))−1) for codeword q can be scrambled, resulting in a block ofscrambled bits {tilde over (b)}^((q))(0), . . . , {tilde over(b)}^((q)(M) _(bit) ^((q))−1), according to the following equation,where M^((q)) _(bit) is the number of bits in codeword q.{tilde over (b)} ^((q))(i)=(b ^((q))(i)+c ^((q))(i))mod 2  [Equation 11]

where the scramble sequence c^((q))(i) can be given by Equation 7. Thescrambling sequence generator is initialized at the start of eachsubframe. In case of a transport block for PDSCH, the initializationvalue c_(init) is given by the following equation.c _(init) =n _(RNTI)·2¹⁴ +q·2¹³ +└n _(s)/2┘·2⁹ +N _(ID)^(cell)  [Equation 12]

In the present invention, a UE operating in the coverage enforcementmode may apply the MTC-SI-RNTI to n_(RNTI) in Equation 12.

Regarding Procedure 2), a transmission block to be transmitted throughthe PDSCH is subjected to transmission block processing, transmissionblock CRC attachment, code block segmentation and code block CRCattachment, channel coding, and rate matching and code blockconcatenation before mapping to a PDSCH. Error detection is applied tothe transmission block or code block through the CRC. The entiretransmission block or entire code block is used in calculating CRCparity bits to be attached thereto. In the present invention, theMTC-SI-RNTI or the C-RNTI may be used to calculate CRC parity bits. Inaddition, the CRC parity bits calculated using the MTC-SI-RNTI or theC-RNTI may be added to a transmission block or a code blockcorresponding to a higher layer signal according to an embodiment of thepresent invention. Let's assume that the MTC-SI-RNTI or the C-RNTI isa₀, a₁, a₂, a₃, . . . , a_(A−1) and the CRC parity bits are b₀, b₁, b₂,b₃, . . . , b_(L−1) where A is the length of the MTC-SI-RNTI or theC-RNTI and L is the number of parity bits. The CRC parity bits may begenerated, for example, by one of the following cyclic generatorpolynomials.g _(CRC24A)(D)=[D ²⁴ +D ²³ ±D ¹⁸ +D ¹⁷ +D ¹⁴ +D ¹¹ +D ¹⁰ +D ⁷ +D ⁶ +D ⁵+D ⁴ +D ³ +D+1]  [Equation 13]g _(CRC24B)(D)=[D ²⁴ +D ²³ +D ⁶ +D ⁵ +D+1]  [Equation 14]

Herein, g_(CRC24A) represents a cyclic generator polynomial forgenerating 24 parity bits to be attached to the transmission block as aCRC, and g_(CRC24B) represents a cyclic generator polynomial forgenerating 24 parity bits to be attached to the code block as a CRC.Encoding is performed in a systematic form, which means that, in GaloisField of 2, GF(2), the polynomial ‘a₀D^(A+23)a₁D^(A+22)+ . . .a_(A−1)D^(A+24)+p₀D²³+p₀D²²+ . . . +p₂₂D¹+p₂₃’ yields a remainder equalto 0 when the polynomial is divided by the corresponding length-24 CRCgenerator polynomial, g_(CRC24A) or g_(CRC24B).

Alternatively, the CRC may be calculated using Equation 13 and Equation14 with respect to all transmission blocks or all code blocks to whichthe CRC will be added and the calculated CRC may be scrambled with theMTC-SI-RNTI or the C-RNTI and then added to a corresponding transmissionblock or code block. For example, CRC parity bits b₀, b₁, b₂, b₃, . . ., b_(L−1) may be scrambled with x_(rnti,0), x_(rnti,1), x_(rnti,2), . .. , x_(rnti,C−1) which is the MTC-SI-RNTI or the C-RNTI according to thefollowing equation.c _(k)=(b _(k) +x _(rnti,k))mod 2 for k=0,1,2, . . . ,C−1  [Equation 15]

where x_(rnti,0) is the most significant bit of the MTC-SI-RNTI or theC-RNTI and C denotes the length of the MTC-SI-RNTI or the C-RNTI.

In relation to process 3), the MTC-SI-RNTI or the C-RNTI may be appliedto a scrambling ID n_(SCID) of Equation 12. Since the UE is aware of theMTC-SI-RNTI or the C-RNTI used as the scrambling ID used to generate aUE-RS, the UE may be aware of a UE-RS sequence transmitted together witha PDSCH and may decode the PDSCH using the UE-RS sequence, therebyacquiring a higher layer signal carried by the PDSCH.

Upon receipt of a UE-specific PDSCH bundle, the UE may transmit A/Ninformation for PDSCH reception using a UL resource to the eNB after G3subframes. In this case, G3 may be 4 or may be the same value as a valuewhen subframe bundling for a PDSCH/PUSCH is not configured and the A/Ninformation may be transmitted through a bundle of A1 UL subframes.Alternatively, the UE may receive A/N information for a PUSCH through abundle of A2 UL subframes starting from a subframe after G3 subframessince the entire PUSCH bundle has been transmitted to the eNB. The valueG3 and A1 may be fixed or may be configured for the UE through an MID,an SIB, or a higher layer such as an RRC signal.

The PDSCH bundle transmission period, PDSCH bundle transmission offset,and/or PDSCH bundle size described in embodiment B of the presentinvention may be used not only for reservation/configuration ofsubframes for PDSCH transmission but also for reservation/configurationof subframes for bundle transmission of other physical channels. Forexample, the bundle transmission period, the bundle transmission offset,and/or the subframe bundle size may be used for reservation of subframesfor repetitive transmission, i.e. for configuration of a subframebundle, of physical channels (e.g. a PDCCH, a PBCH, a PUCCH, a PUSCH, aPHICH, etc.) in embodiment A and embodiments C to G of the presentinvention.

<C. Shortened PDCCH>

FIG. 14 illustrates a signal transmission/reception method according toembodiment C of the present invention.

When repetitive transmission of a PDCCH is performed in order tosuccessfully transmit the PDCCH to an MTC UE with a coverage issue,there is a problem of remarkably increasing transmission delay andenergy consumption for repetitive transmission. To solve this, thepresent invention proposes transmitting, to the MTC UE with the coverageissue, a shortened PDCCH containing only information indicating whethera PDSCH is transmitted or a shortened PDCCH information indicatingwhether a PDSCH is transmitted. The UE may receive less information onlyindicating whether the PDSCH is transmitted thereto through theshortened PDCCH and, if the PDSCH is transmitted thereto, the UE mayreceive data through a determined PDSCH resource or region (hereinafter,resource/region). For example, the shortened PDCCH may include onlyinformation about an ID of the UE (e.g. C-RNTI) at which the PDCCH istargeted. Upon receiving or detecting the PDCCH including theinformation about the UE ID of the UE (e.g. C-RNTI), the UE may assumethat the PDSCH is transmitted thereto.

When the shortened PDCCH is used for data transmission to the MTC UEwith the coverage issue, if a shortened PDCCH for a specific UE (e.g.UE1) is transmitted through a specific subframe as illustrated in FIG.14(a), a PDSCH may be transmitted through a bundle of D subframesstarting from a subframe with the shortened PDCCH. In UL, if a shortenedPDCCH for a specific UE is transmitted through a specific subframe, theUE that has received the shortened PDCCH may transmit a PUSCH throughthe bundle of D subframes starting from the fourth subframe after thespecific subframe. The shortened PDCCH may include information about thenumber of subframes in which the PDSCH is transmitted, i.e. about thesize D of a PDSCH bundle.

The UE that has received the shortened PDCCH may receive datatransmitted thereto through a determined PDSCH resource/region. In orderto designate the PDSCH resource/region and transmit data through thePDSCH resource/region, the schemes mentioned in embodiment B of thepresent invention as described above may be applied. The PDSCHresource/region may be cell-specific or UE-specific. In addition, thePDSCH resource/region for transmitting cell-specific data, such as anSIB, may be cell-specifically designated. The PDSCH resource/region fortransmission of UE-specific data such as transmission of data for aspecific UE may be cell-specifically designated or UE-specificallydesignated.

Alternatively, the PDSCH resource/region for the MTC UE with thecoverage issue may be determined according to a PDCCH resource/region inwhich the shortened PDCCH is transmitted. For example, the PDSCHresource/region determined according to the PDCCH resource/region may bepresent as illustrated in FIG. 14(b). For example, the PDSCH resourcemay be determined according to a PDCCH candidate index or a CCE index ofa PDCCH (e.g. an index of the first CCE among CCEs included in thePDCCH). Referring to FIG. 14(b), when the UE receives the shortenedPDCCH transmitted thereto through a PDCCH 1 resource/region, the UE mayreceive data through a PDSCH resource/region associated with PDCCH 1and, when the UE receives the shortened PDCCH transmitted to the UEthrough a PDCCH 2 resource/region, the UE may receive data through aPDSCH resource/region associated with the PDCCH 2 resource/region. Forexample, the UE may be aware of a PDSCH resource linked to a PDCCH basedon a resource index of the PDCCH.

Upon receiving a UE-specific PDSCH bundle, the UE may transmit A/Ninformation for PDSCH reception to the eNB using a UL resource after G3subframes. In other words, the UE may transmit the A/N information tothe eNB using a resource for A/N transmission in the G3-th subframeafter receiving the UE-specific PDSCH bundle. The value G3 may be 4 ormay be the same value as a value in the case in which subframe bundlingfor the PDSCH/PUSCH is not configured. The A/N information may betransmitted through a bundle of A1 UL subframes. Alternatively, the UEmay receive the A/N information for the PUSCH through a bundle of A2 ULsubframes starting from a subframe which follows G3 subframes aftertransmitting the entire PUSCH bundle to the eNB (i.e. from the G3-thsubframe after transmitting the entire PUSCH bundle). The values G3 andA1 may be fixed values or may be configured for the UE through an MID,an SIB, or a higher layer signal such as an RRC signal.

<D. Conflict Issue Between PDCCH and PDSCH>

FIGS. 15, 16, and 17 illustrate signal transmission/reception methodsaccording to embodiment D of the present invention. Embodiment D of thepresent invention may be applied together with at least one ofembodiment A and embodiments C to G of the present invention.

As mentioned above, for the MTC UE, a PDCCH may be transmitted in theform of a PDCCH bundle through a plurality of consecutive ornon-consecutive subframes and transmission of such a PDCCH bundle may bestarted at a predetermined or preconfigured subframe location. In thiscase, a subframe in which the UE should receive a PDSCH bundle mayoverlap with a subframe in which transmission of a new PDCCH bundle canbe started.

Then, the UE may assume that a new PDCCH (that the UE should receive) isnot transmitted while the UE receives one PDSCH bundle as illustrated inFIG. 15(a).

Alternatively, when a subframe in which the PDSCH bundle should bereceived overlaps with a subframe in which transmission of the new PDCCHbundle can be started, the UE may stop receiving the PDSCH bundle thatthe UE receives and attempt to receive the new PDCCH bundle, asillustrated in FIG. 15(b). Alternatively, the UE may stop receiving thePDSCH bundle that the UE receives and may not attempt to receive a PDCCHbundle under the assumption that a PDCCH bundle for another UE can betransmitted in a duration during which a PDCCH bundle can betransmitted. After receiving a PDCCH bundle or after a subframe in whicha PDCCH bundle is transmitted, the UE may continue to receive the PDSCHbundle that the UE has temporarily stopped receiving. When the UE stopsreceiving the PDSCH bundle and attempts to receive the new PDCCH bundledue to overlap between a subframe in which the UE should receive thePDSCH bundle and a subframe in which transmission of the new PDCCHbundle can be started, the eNB may not transmit a DL grant to the UE inthe corresponding PDCCH bundle and may transmit only a UL grant. The UEmay assume that the DL grant is not transmitted in the correspondingPDCCH bundle.

When a PDCCH is transmitted in the form of a PDCCH bundle for the MTC UEand transmission of the PDCCH bundle is started at a predeterminedsubframe location, a subframe for transmission of a PUSCH bundle mayoverlap with a subframe in which transmission of a new PDCCH bundle isstarted. In this case, the UE may assume that the PDCCH that the UEshould receive is not transmitted in a duration during which the PUSCHbundle is transmitted as illustrated in FIG. 16(a). Alternatively, iftimings of a subframe for transmission of the PDSCH bundle and asubframe for transmission of the new PDCCH bundle overlap, i.e. if PUSCHbundle transmission and new PDCCH bundle transmission collide, the UEmay transmit the PUSCH bundle and simultaneously attempt to receive thenew PDCCH bundle as illustrated in FIG. 16(b). In this case, the UE mayassume that a UL grant is not transmitted thereto through a PDCCH bundlecolliding with a PUSCH bundle transmission timing. Alternatively, the UEmay transmit the PUSCH bundle and simultaneously attempt to receive thenew PDCCH bundle. The UE may assume that the UL grant is not transmittedthereto if transmission of the PDCCH bundle is ended before transmissionof the PUSCH bundle is ended. Alternatively, the UE may assume that theUL grant is not transmitted thereto if transmission of the PDCCH bundleis ended prior to X (e.g. X=4) subframes starting from a subframe inwhich transmission of the PUSCH bundle is ended.

Meanwhile, as illustrated in FIG. 17, the length of the PDCCH bundle maybe greater than a spacing between subframe locations at whichtransmission of the PDCCH bundle can be started. In this case, if the UEdoes not simultaneously receive different PDCCH bundles, the UE mayassume that only one PDCCH is transmitted thereto at a time.

<E. Conflict Issue Between PBCH and PDSCH>

FIG. 18 illustrates a signal transmission/reception method according toembodiment E of the present invention.

As described above, for an MTC UE requiring coverage enhancement, aPDSCH may be transmitted through a plurality of consecutive ornon-consecutive subframes. Similarly, a PBCH may be transmitted throughmultiple subframes for coverage enhancement of the MTC UE. In the firstsubframe #0 of each 10 ms radio frame, as illustrated in FIG. 18(a), inaddition to an existing PBCH transmitted in 6 center RBs of 4 OFDMsymbols (OFDM symbols #7 to #10), an additional PBCH may be transmittedin a subframe in which the existing PBCH is not transmitted (e.g.subframes #1 to #9 of each 10 ms radio frame). In this case, a PBCH inan additional subframe may be transmitted through an RE resource onwhich the existing PBCH is transmitted as illustrated in FIG. 18(a) ormay be transmitted through all OFDM symbol resources/regions except fora PDCCH resource/region in the corresponding subframe as illustrated inFIG. 18(b). Hereinafter, in the present invention, a PBCH for the MTC UEperforming coverage enhancement transmitted in an additional subframeother than a conventionally transmitted PBCH will be referred to as anadditional PBCH.

When a PBCH is transmitted through multiple subframes for the MTC UErequiring coverage enhancement, a legacy UE does not know presence of anadditional PBCH transmitted through subframes in which an existing PBCHhas not been transmitted. Accordingly, when the eNB transmits a PDSCH(or EPDCCH) to the legacy UE in a subframe in which the additional PBCHfor the MTC UE performing coverage enhancement is transmitted, the eNBperforms scheduling of the PDSCH (or EPDCCH) avoiding a PRBresource/region (e.g. 6 center PRBs) in which the additional PBCH istransmitted.

If the eNB transmits the PDSCH (or EPDCCH) to the MTC UE in a subframein which the addition PBCH is transmitted when the PBCH is transmittedthrough a plurality of subframes for the MTC UE requiring coverageenhancement, the eNB may perform scheduling of the PDSCH (or EPDCCH)avoiding the PRB resource/region (e.g. 6 center PRBs) in which theadditional PBCH is transmitted.

When the PBCH is transmitted through multiple subframes for the MTC UErequiring coverage enhancement, the MTC UE may be aware of the fact thatthe additional PBCH is transmitted and of a transmission resource onwhich the additional PBCH is transmitted. If PRB resources/regions inwhich the additional PBCH and the PDSCH are transmitted overlap when thePDSCH is transmitted to the MTC UE, the eNB may not transmit the PDSCHto the MTC UE in a corresponding subframe. For example, the UE mayassume that, if the PRB resources/regions of the additional PBCH and thePDSCH overlap, the PDSCH is not transmitted in a corresponding subframe.That is, the UE may not expect that the PDSCH will be transmitted in asubframe in which transmission of the additional PBCH and transmissionof the PDSCH collide. Alternatively, if the PRB resources/regions of theadditional PBCH and the PDSCH overlap when the PDSCH is transmitted tothe MTC UE, the eNB may rate-match the PDSCH with respect to an REresource/region in which the additional PBCH is transmitted in acorresponding subframe and transmit the rate-matched PDSCH to the MTCUE. Namely, if the PRB resources/regions of the additional PBCH and thePDSCH overlap, the UE may assume that the PDSCH is rate-matched withrespect to the additional PBCH resource/region in a correspondingsubframe and then transmitted.

<F. Number of Repetitions of PDCCH and PDSCH>

FIG. 19 illustrates a signal transmission/reception method according toembodiment F of the present invention.

The number of repetitions of a PDCCH transmitted by the eNB to the MTCUE may be differently configured per UE or may be cell-specificallyconfigured, at an access initial step. Alternatively, the number ofrepetitions of the PDCCH may be semi-statically changed through RRCconfiguration. Then, the UE may perform decoding under the expectationthat a repeatedly transmitted PDCCH will be transmitted a specificnumber of times. However, in order to reduce scheduling flexibility andsignaling overhead of the eNB, the eNB may transmit the PDCCH throughfewer repetitions than the number of repetitions of the PDCCH (or amaximum number of repetitions of the PDCCH) which is indicated to the UEor determined according to a value necessary for coverage enhancement ofthe UE, as illustrated in FIG. 19. In this case, the UE may assume thata PDCCH bundle can be transmitted through fewer repetitions than thenumber of repetitions of the PDCCH (or a maximum number of repetitionsof the PDCCH) which is configured by the eNB for the UE or determinedaccording to the value necessary for coverage enhancement of the UE. Forexample, the eNB may flexibly transmit the PDCCH through repetitionsequal to or less than the number of repetitions of the PDCCH expected bythe UE according to a channel environment of the UE or schedulingrestrictions. In this case, since the UE does not know a bundle size ofan actually transmitted PDCCH, the UE may attempt to decode the PDCCH inevery subframe.

Meanwhile, the number of repetitions of a PDSCH may be differentlyconfigured per UE or may be cell-specifically configured, at an accessinitial step. Alternatively, the number of repetitions of the PDSCH maybe semi-statically changed through RRC configuration. Alternatively, thenumber of repetitions of the PDSCH may be configured through a PDCCHwhenever the PDSCH is transmitted. However, in order to reducescheduling flexibility and signaling overhead of the eNB, the eNB maytransmit the PDSCH through fewer repetitions than the number ofrepetitions of the PDSCH (or a maximum number of repetitions of thePDSCH) which is indicated to the UE or determined according to the valuenecessary for coverage enhancement of the UE. In this case, the UE mayassume that a PDSCH bundle can be transmitted through fewer repetitionsthan the number of repetitions of the PDSCH (or a maximum number ofrepetitions of the PDSCH) which is configured by the eNB for the UE ordetermined according to the value necessary for coverage enhancement ofthe UE. For example, the eNB may flexibly transmit the PDSCH throughrepetitions equal to or less than the number of repetitions of the PDSCHexpected by the UE according to a channel environment of the UE orscheduling restrictions. In this case, since the UE does not know abundle size of an actually transmitted PDSCH, the UE may attempt todecode the PDSCH in every subframe.

In addition, the eNB may inform the UE of a minimum number ofrepetitions of the PDCCH/PDSCH. Alternatively, the minimum number ofrepetitions of the PDCCH/PDSCH may be a fixed value or a predefinedvalue.

When it is difficult for the UE to successfully receive data over onePDCCH/PDSCH, if the UE is not aware of an accurate number of repetitionsof the PDCCH/PDSCH transmitted by the eNB, the UE attempts to receivethe PDCCH/PDSCH using PDCCH/PDSCH subframes up to a maximum number ofrepetitions. However, if the UE attempts to receive the PDCCH/PDSCH inthe PDCCH/PDSCH subframes up to the maximum number of repetitions, sincesignals of more subframes than a number of repetitions of thePDCCH/PDSCH actually transmitted by the eNB, values that hinder decoding(e.g. data for other UEs or undesired signals) may be frequently usedfor decoding.

However, when the UE is aware of a minimum number of repetitions of thePDCCH/PDSCH according to the present invention, if HARQ is applied to DLdata, the UE may use only the PDCCH/PDSCH corresponding to a minimumnumber of times for decoding although the UE does not know an accuratenumber of repetitions of the PDCCH/PDSCH transmitted by the eNB. In thiscase, values that hinder decoding (e.g. data for other UEs or undesiredsignals) are not frequently used. If the UE fails to perform decodingalthough the UE has attempted to decode data using the PDCCH/PDSCHsubframes up to the maximum number of repetitions (e.g. when a decodingresult is determined to be NACK), the UE may (combine and) store onlydata transmitted in the PDCCH/PDSCH subframes corresponding to theminimum number of repetitions in a reception HARQ buffer.

The eNB may 1) inform the UE of both maximum and minimum numbers ofrepetitions and configure the UE to enable a HARQ combining operation(described above) or 2) configure the UE to disable the HARQ combiningoperation instead of informing the UE of the maximum number ofrepetitions. Alternatively, similarly, the UE may be configured (by theeNB) to 1) automatically enable the HARQ combining operation (describedabove) when both the maximum and minimum numbers of repetitions aregiven or 2) automatically disable the HARQ combining operation if onlythe maximum number of repetitions is given.

<G. Independent Transmission Timing of PDCCH, PDSCH/PUSCH, and ACK/NACK>

FIG. 20 illustrates a signal transmission/reception method according toembodiment G of the present invention.

As in the case in which the location and period of a subframe in whichtransmission of a PDCCH bundle for the MTC UE can be started can bedetermined, the start locations and periods of a subframe bundle forPDSCH/PUSCH transmission and a subframe bundle for ACK/NACK (e.g. PUCCHor PHICH) transmission for data may be determined. Characteristically,information about subframe locations and subframe durations in whichtransmission of PDCCH, PDSCH/PUSCH, PHICH, and PUCCH bundles is startedmay be independently configured. For example, when a subframe in whichtransmission of the PDCCH bundle can be started is subframe n, n may bea value satisfying (n mod D1)=G1 where D1 denotes a period of a subframein which PDCCH transmission can be started and G1 denotes an offset of asubframe location at which PDCCH transmission can be started. Forexample, G1 denotes the location of a PDCCH transmission start subframein a duration of DI. Similarly, if a transmission start subframe of thePDSCH bundle is subframe k and a transmission start subframe of thePUCCH bundle is subframe m, then k and m may be values satisfying (k modD2)=G2 and (m mod D3)=G3, respectively. In this case, D2 denotes aperiod of a subframe in which PDSCH transmission can be started, G2denotes an offset of a subframe location at which PDSCH transmission canbe started, D3 denotes a period of a subframe in which PUSCHtransmission can be started, and G3 denotes an offset of a subframelocation at which PUSCH transmission can be started. The values D1, G1,D2, G2, D3, and G3 may be independently determined.

In this case, as illustrated in FIG. 20, upon receiving the PDCCH bundlefor scheduling a PDSCH from the eNB, the UE may receive the PDSCH bundlestarting from the nearest subframe among subframes in which transmissionof the PDSCH bundle can be started, which are located after X1 subframesstarting from a subframe in which transmission of the PDCCH bundle isstarted. Similarly, in order for the UE that has received the PDSCHbundle to transmit ACK/NACK information for the corresponding PDSCHthrough a PUCCH, the UE may transmit the PUCCH bundle starting from thenearest subframe among subframes in which transmission of the PUCCHbundle can be started, which are located after X2 subframes startingfrom a subframe in which transmission of the PDCCH bundle is started. Inthis case, X1 and/or X2 may be pre-defined values or may be valuesconfigured by the eNB.

In the above-described embodiments of the present invention, in order totransmit data and signals suitable for a channel situation to the MTCUE, the eNB needs to distinguish an MTC UE with a coverage issue from anMTC UE without a coverage issue. However, the eNB does not know presenceof the UE until the UE transmits a PRACH. Accordingly, since the eNBdoes not know presence of the UE until the UE receives an SIB for thefirst time, the UE according to the present invention may determinewhether the UE has a coverage issue. For example, the UE may determinewhether the UE has a coverage issue using at least one of {circle around(1)} time, the number of subframes, and/or the number of PSSs/SSSsneeded to successfully receive a PSS/SSS, {circle around (2)} time, thenumber of subframes, and/or the number of PBCHs needed to successfullyreceive a PBCH, {circle around (3)} a result obtained by performing aradio resource management (RRM) (e.g. a reference signal received power(RSRP)), and {circle around (4)} time and/or the number of subframesneeded to successfully receive an SIB, and/or success/failure ofreception of the SIB attempted during a specific time duration. If it isdetermined that the MTC UE has a coverage issue, the MTC UE may informthe eNB that the MTC UE has a coverage issue by applying a coverageenhancement scheme according to the embodiment(s) of the presentinvention or transmitting a PRACH defined to indicate the coverageenhancement scheme. Meanwhile, the eNB does not know presence or absenceof the UE with a coverage issue before the UE with a coverage issueinforms the eNB that the UE has a coverage issue through PRACHtransmission (explicitly or implicitly) indicating the coverage issue orbefore the UE with a coverage issue completes initial access to the eNB.Therefore, the eNB according to the present invention (even if the eNBcannot recognize the MTC UE with a coverage issue) may perform subframebundle transmission according to the present invention for the MTC UErequiring coverage enhancement. If the UE transmits the PRACH andcompletes initial access to the eNB, the eNB may determinepresence/absence of the UE with a coverage issue, a coverage enhancementlevel, etc. (through RRM information, etc.) and inform the UE of adetermined result.

Embodiments A to G of the present invention may be separately applied ortwo or more thereof may be applied together.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 20 in UL and as the transmitting device 10 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

For example, the eNB processor may control the eNB RF unit so that aPDCCH, a PDSCH, a PHICH, and/or a PBCH may be (repeatedly) transmittedaccording to any one of embodiments A to G of the present invention. TheeNB processor may control the eNB RF unit so that a PUCCH and/or a PUSCHtransmitted by the UE may be (repeatedly) received according to any oneof embodiments A to G of the present invention. The eNB processor may(combine and) decode the repeatedly received PUCCH and/or PUSCH. The eNBprocessor may generate ACK/NACK information according to whetherdecoding has successfully been performed and control the eNB RF unit sothat the ACK/NACK information may be transmitted through the PHICH. TheeNB processor may control the eNB RF unit so as to perform repetitivetransmission of the PHICH. The eNB processor may control the eNB RF unitso that configuration information of a subframe bundle (e.g. atransmission period, a transmission offset, a start frame, a bundlesize, and/or a number of repetitions) may be transmitted for repetitivetransmission of the PDCCH, PDSCH, PUCCH, PUSCH, PHICH and/or PBCH. TheeNB processor may control the eNB RF unit so that (repetitive)transmission/reception of a corresponding physical channel may beperformed in a corresponding bundle based on the configurationinformation.

The UE processor may control the UE RF unit so that a PDCCH, a PDSCH, aPHICH, and/or a PBCH may be (repeatedly) received according to any oneof embodiments A to G of the present invention. The UE processor maycontrol the UE RF unit so that a PUCCH and/or a PUSCH may be(repeatedly) transmitted according to any one of embodiments A to G ofthe present invention. The UE processor may (combine and) decode therepeatedly received PDCCH and/or PDSCH. The UE processor may generateACK/NACK information according to whether decoding has successfully beenperformed and control the UE RF unit so that the ACK/NACK informationmay be transmitted through the PUCCH and/or the PUSCH. The UE processormay control the UE RF unit so as to perform repetitive transmission ofthe PUCCH and/or the PUSCH. The UE processor may control the UE RF unitso that configuration information of a subframe bundle (e.g. atransmission period, a transmission offset, a start frame, a bundlesize, and/or a number of repetitions) may be received for repetitivetransmission of the PDCCH, PDSCH, PUCCH, PUSCH, PHICH and/or PBCH. TheUE processor may control the UE RF unit so that (repetitive)transmission/reception of a corresponding physical channel may beperformed in a corresponding bundle based on the configurationinformation.

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to an eNB, a UE,or other devices in a wireless communication system.

The invention claimed is:
 1. A method for receiving, by a userequipment, downlink data, the method comprising: repeatedly receiving,by the user equipment, a physical downlink control channel (PDCCH)carrying downlink control information multiple times across Nconsecutive subframes, where N is an integer greater than 1; andrepeatedly receiving, by the user equipment, a physical downlink sharedchannel (PDSCH) carrying the downlink data multiple times, across Dconsecutive subframes starting from a subframe n+k after a subframe n,based on the downlink control information, wherein the subframe n iswithin the N consecutive subframes, and the subframe n is a subframewhere the PDCCH is received last, wherein the downlink controlinformation includes repetition number information for the PDSCH, and Dis an integer determined based on the repetition number information, andwherein k is an integer greater than
 0. 2. The method according to claim1, further comprising: receiving, by the user equipment, a higher layersignal including information on a maximum number of repetitions for thePDCCH, wherein N is less than or equal to the maximum number ofrepetitions for the PDCCH.
 3. The method according to claim 1, furthercomprising: receiving, by the user equipment, information on a start ofthe N consecutive subframes.
 4. The method according to claim 1, whereinthe repeatedly received PDCCH is received using a same control channelelement (CCE) resource within the N consecutive subframes.
 5. A methodfor transmitting, by a base station, downlink data, the methodcomprising: repeatedly transmitting, by the base station, a physicaldownlink control channel (PDCCH) carrying downlink control informationmultiple times across N consecutive subframes, where N is an integergreater than 1; and repeatedly transmitting, by the base station, aphysical downlink shared channel (PDSCH) carrying the downlink datamultiple times, across D consecutive subframes starting from a subframen+k after a subframe n, based on the downlink control information,wherein the subframe n is within the N consecutive subframes, and thesubframe n is a subframe where the PDCCH is transmitted last, whereinthe downlink control information includes repetition number informationfor the PDSCH, and D is an integer determined based on the repetitionnumber information, and wherein k is an integer greater than
 0. 6. Themethod according to claim 5, further comprising: transmitting, by thebase station, a higher layer signal including information on a maximumnumber of repetitions for the PDCCH, wherein N is less than or equal tothe maximum number of repetitions for the PDCCH.
 7. The method accordingto claim 5, further comprising: transmitting, by the base station,information on a start of the N consecutive subframes.
 8. The methodaccording to claim 5, wherein the repeatedly transmitted PDCCH istransmitted using a same control channel element (CCE) resource withinthe N consecutive subframes.
 9. A user equipment for receiving downlinkdata, the user equipment comprising: a transceiver unit, and a processorconfigured to control the transceiver to: repeatedly receive a physicaldownlink control channel (PDCCH) carrying downlink control informationmultiple times across N consecutive subframes, where N is an integergreater than 1; and repeatedly receive a physical downlink sharedchannel (PDSCH) carrying the downlink data multiple times, across Dconsecutive subframes starting from a subframe n+k after a subframe n,based on the downlink control information, wherein the subframe n iswithin the N consecutive subframes, and the subframe n is a subframewhere the PDCCH is received last, wherein the downlink controlinformation includes repetition number information for the PDSCH, and Dis an integer determined based on the repetition number information, andwherein k is an integer greater than
 0. 10. The user equipment accordingto claim 9, wherein the processor is configured to control thetransceiver to receive a higher layer signal including information on amaximum number of repetitions for the PDCCH, wherein N is less than orequal to the maximum number of repetitions for the PDCCH.
 11. The userequipment according to claim 9, wherein the processor is configured tocontrol the transceiver to receive information on a start of the Nconsecutive subframes.
 12. The user equipment according to claim 9,wherein the repeatedly received PDCCH is received using a same controlchannel element (CCE) resource within the N consecutive subframes.
 13. Abase station for transmitting downlink data, the base stationcomprising: a transceiver unit, and a processor configured to controlthe transceiver to: repeatedly transmit a physical downlink controlchannel (PDCCH) carrying downlink control information multiple timesacross N consecutive subframes, where N is an integer greater than 1;and repeatedly transmit a physical downlink shared channel (PDSCH)carrying the downlink data multiple times, across D consecutivesubframes starting from a subframe n+k after a subframe n, based on thedownlink control information, wherein the subframe n is within the Nconsecutive subframes, and the subframe n is a subframe where the PDCCHis transmitted last, wherein the downlink control information includesrepetition number information for the PDSCH, and D is an integerdetermined based on the repetition number information, and wherein k isan integer greater than
 0. 14. The base station according to claim 13,wherein the processor is configured to control the transceiver totransmit a higher layer signal including information on a maximum numberof repetitions for the PDCCH, wherein N is less than or equal to themaximum number of repetitions for the PDCCH.
 15. The base stationaccording to claim 13, further comprising: wherein the processor isconfigured to control the transceiver to transmit information on a startof the N consecutive subframes.
 16. The base station according to claim13, wherein the repeatedly transmitted PDCCH is transmitted using a samecontrol channel element (CCE) resource within the N consecutivesubframes.